When characters reach a very high level, or for a conceptual game with a very high fantasy scope, the thought and need to explore alternate realms or dimensions within a fantasy universe becomes attractive. It expands the scope of the world beyond the world map, thus allowing new places and things to be added into the game. Plus it can also be accompanied by a huge powering down of the party, as they lose access to both their knowledge and many of their social resources. This is true even with access to things like constant, permanent portals within worlds as time to travel in the new dimension and the friction between the cultures will mean your social clout is worth much less in an exploratory style of game.
(Of course, I've never gotten to that point, and I doubt many of you have either. It can be hard enough playing in a regular group, much less getting a group that actually plays together in the same campaign with the same characters to actually get to that level. Still fun to think about conceptually.)
In short, dimensions offer up new dangers and opportunities to explore. The only way to explore these places with any degree of success or safety is to bring along some very special equipment, spells, and strong hirelings and other help for your mission. Every year spent preparing for the journey (or every season if the entire group is max level or mythically powerful and resourceful) roll once on the relevant table for resources you are seeking. You can also set up special industries in the dimensions as well, which could be incredibly profitable.
 The Silver Dish - 2nd level
This spell requires a silver dish to be cast. The dish can be large enough to hold 2 rations worth of fruits, bread, meat, and so on- but can be smaller if resources are not available. When this spell is cast, it magically filters and selects food items plucked, sorted, and gathered nearby the dish into the dish if they are edible and safe to members of a specific species. The species is whoever made the silver dish, and while this is usually the same as the spellcaster, occasional exploration parties have gotten wiped out when some very alcoholic mushrooms showed up on a Dwarven Dish; inedible to their human users. This spell also only sorts the food and shows what is safe to eat, meaning non of the food may be chosen, and not detecting any secondary nonlethal effects such as mutations.
 Nullify Acid - 2nd level
This spell stops the corrosive effects of a single type of acid against a single person and everything they are wearing. It can also be cast on a barrel or small cart full of items which will all be protected, or a single larger object like a chest. The spell lasts one day, but offer no protection against other acids or corrosive effects.
 Abstractus - 3rd level
This is a form of mental and magical combat that allows Wizards to duel even from different home universes. While in many worlds, the cultural importance of Wizard duels to create hierarchies or force compliance with some new law or to give up some wealth or power to an upstart is very common; the actual laws and schools of magic are as wide and varied as the ocean. When an elemental Wizard has to perform a ritualized, nonlethal Wizard's duel against a Necromancer-Aligned Sorceress of the Sixth Seal, this becomes a huge issue. As such, this spell allows the user to create an arena made of 99% mind and 1% magic, allowing Wizards to duel for dominance within it. Use your favorite magic dueling rules, or just allow attack rolls with a d20 using Intelligence as a bonus for offense and Wisdom from defense. First to three strikes wins.
 The Supreme Sign - 4th level
This is a magic sign, which must be crafted by the caster. At least the text written or inscribed on the sign must be made by their own hand, but little to no artistic or writing skill is required. As long as the sign has some kind of message to be told, the spell will function. When cast, the sign is imbued with a supernatural ability to communicate whatever is written on it in any language. While many spells exist that allow the user to speak all spoken tongues, this applies to all languages including esoteric ones such as magical signals, energy waves, pheromones and hand signs, dances, and all other sorts of methods of communication used by intelligent creatures across the multiverse- anyone or anything that can speak one language that sees the sign understands what its saying. The effect of this spell is permanent, but the sign could be knocked down or vandalized to end the spell.
 Protection from All Elements - 4th level
This spell protects up to 20 people from the environment. Where as a more mundane, lower spell-level version of this spell may only protect from earthly environments such as hot deserts or cold tundras, this spell is much more powerful. It protects from extremely hot, oven-like deserts, blisteringly cold places, places with intense and otherwise crippling static electricity, as well as places with an acidic atmosphere or utterly aggressive plant life. It can also minorly protect from the effects of positive or negative energy auras, as well as things like realms too bathed in sunlight or with carnivorous darkness, as long as these effects are mild. This only protects against the environment, but does grant +2 to saves from all elemental spells. It lasts three days.
Additionally, this spell has enough juice in it to instead be cast on a very large object instead. This is almost always a ship, a massive wagon pulled by two elephants (spell also protects the elephants), a walking house, etc. This spell can therefore be used to protect you on voyages over the boiling acid oceans or even through the astral realm while flying on writhing galaxies of emotion; but it offers no protection to the crew unless cast twice.
 Garden of Eden - 4th level
This spell creates a small sanctified area of land. The area of land is roughly the size of a small forest glade, large enough to support a decent sized vegetable garden with a few crops in space. This area is magically protected from outside harmful winds, miasmas, pests, and other environmental effects that would negatively impact the space from this dimension. It offers no protection against intelligent beings or animals, but will happily allow growth of non-intrusive native plants and beings as well.
The Garden of Eden spell is permanent. The land can only be destroyed or returned to the natural state of this alternate reality through ritual desecration; salting the earth, piking the head of its creator and burning it down, etc. Otherwise, Gardens created by this spell are some of the few safe havens in other worlds.
 Vensin's Oubliette - 5th level
Avoiding local fauna tends to be pretty easy while exploring outer realms. With the ability to shift or travel between worlds, avoiding local problems and enemies is as simple as leaving your operation to another dimensional plane of reality. However, certain beings and monsters are not so easily deterred. Beings that exist between dimensions, or those with the power to shift between worlds themselves, can pursue beings beyond several realms. Certain beings such as Elder Gods or powerful entities of the outside can also reach and 'see' their way into worlds to seek their foes.
For this purpose, Vensin's Oubliette was created. It is a spell that banishes a single being into an alternate, hopeless dimension known as the Oubliette. This spell requires a bottomless pit and the victim to be pushed in, or hovering over it, in which case it slowly sucked them down. It then transfers them into another dimension. It's a dark hole that can never be climbed out of, and has no food or life to speak beyond a single trickle of water that occasionally drips down from above. The Oubliette's main ability is that its locked away in a separate prison dimension meant to keep being in. Once banished to this place, any normal mortal being will eventually die from starvation and lack the means to escape. Some interdimensional predators can be slain this way; locking them into the Oubliette to avoid them from chasing you any more. Beings with the ability to cast spells or open portals to other worlds under 5th level will not be able to penetrate this dimension's cold stone walls.
Otherworldly beings of higher degrees of power aren't so easily captured. Certain manifestations of stronger beings, such as the avatars of elder gods, may requires help from their “main body” in order to escape. Immortals trapped in this realm will probably go through several cycles of birth and death before managing to slip their soul out of this realm.
 Opalescent Blast - 5th level
Concentrated on a single point or in a general direction, this spell conjures an almighty wave of force. Similar to its weaker version, the Opalescent Wave, this spell emerges a pale white and changes color and elemental affinity to whatever it hits is weakest to. Unlike the Wave spell however, this one is full proof. Every single creatures, being, outsider, or entity that is hit by this spell is struck by its greatest weakness- the spell magically shifts into its counter element. Even things without “weaknesses” can be harmed by this spell, though effects on immortal or invulnerable entities can sometimes be very strange or have disastrous consequences to everyone nearby; an eldritch horror who can only be harmed by radiation will blast back quite a few gamma rays back at your party; who have neither the protection or knowledge with how to deal with that kind of “hex”.
The spell deals 3d6 damage to whatever it hits, and has a range similar to fireball with a guided direction; it can be angled to explode around allies instead of striking them even if adjacent to enemies. It also deals damage equal to the creature's greatest weakness, and the creature takes the negative effects and damage bonus of that element from this spell. If a large opal is used as the channeling stone of this spell, then it deals 4d6 damage instead, and turns into a smooth gray stone.
 The Locking of the Gate - 6th level
This spell can only be activated by being besides each world's gate. The gate is outside of the main world, it could be floating in space or within impassable walls. It could be in the major city of the world, a huge monument to some old victory with hidden purpose. It could be a drawing in a notebook by a mad artist. Regardless of what the gate is, the gate is the door to this world. Once this spell is cast, the gate is closed. This means nothing from that world can enter or leave it again. It is within the caster's power to cast this spell just on the other side of the gate, as they will not be trapped- using this spell, it is possible to section off problem worlds from entering the main one of the campaign, or to trap someone within a dimension with even more permanence then a normal prison-dimension spell. Once the gate is closed, nothing can pass between- not Gods or spirits, not magic messages or telepathic messages; nothing can pass between.
To close the gate is easy, but to open the gate is mythical. In the main campaign world, the three black gates that separated reality from unreality were closed by this spell; and were never opened again. It is unknown if they even could be open; a God cannot command a gate closed by this spell to open; it is beyond their power.
 One Billion Step - 6th level
This spell requires the caster to take a step. The moment they touch the ground with their foot, they can instantly travel as far as they want in that direction. It can be a few feet or perfect, predictable teleportation or it can be one hundred trillion miles to another planet; or a hundred million billion leagues in an infinite realm, just to see what is there. The caster may make up to 6 steps using this spell, and once they are finished the spell ends.
The mind boggling spiritual and metaphysical implications of this spell don't end there- the spell can also be used to step on a piece of ground, mural, or anything else and instantly transport oneself to a similar object or material you wish. You can step on a leaf to appear within the endless dimension of peaceful woodlands, or step on a painting to enter that painting's world or any fictional worlds within that painting. This movement is true and cannot be stopped by anything, save if the Gate to this place has been closed and locked by the magic “Locking of the Gate” spell.
Explorer's Items Table – Roll 1d8
 Alethiometer. It is a compass that points towards the truth, and allows the user to speak with a sort of cosmic demiurge consciousness beyond any known divinity or Pantheon. By holding the compass, the user may gain a Hunch Roll towards a certain topic. The hunch roll is a d20 roll rolled immediately. Later; it can be used in place of a single other roll of any kind, or can be placed on an opponent if the user managed to put the opponent in a spot.
 Sovereign Glue and Universal Solvent. You might end up in an especially slippery or frictional dimension where you need this stuff just to keep a hold of your items, or to keep your feet from sticking to the floor.
 Spyglass of True Seeing. Certain animals or objects in this dimension may be totally invisible to your eyes; unadapted to seeing those colors and shapes. You can still 'see' these things by looking through the spyglass, even if you couldn't describe or comprehend them.
 Magic Maps; especially waterproof and fireproof, with nonrunning and inedible inks. Maps that update to nearby creatures are also extremely useful- but would need to be scribed with a steady and knowledge hand beforehand and only work at a fixed location.
 Ointments. Medical ointments are extremely important for exploring any alternate reality due to the slight and sometimes severe differences between the pH levels of the air, water, and soil in other realms. The places you aren't accustomed to will burn your skin and make you vulnerable for wriggling death worms and other inter-dimensional parasites and medical conditions. Also if you use some First Aid rules, then ointments may be the treatment for elemental damage. This type of damage is very common in the form of storms, spell using wildlife, or raw elemental energies of a dimension.
 Stretchladder. It's a ladder that can go up as much as you want, basically. Every round you hold the button on the side, it extends another 3 ft and a few inches. Every 3 rounds, consider it having grown 10 ft. Over the course of the turn, you can make it grow up to 100 ft. It's made of a silvered metal and if it is broken at any point the entire thing shatters into ultra-thin shards stretched across its vast distance. It isn't especially sturdy or strong, and can be buffeted down by strong winds.
 Halfling Wonderbag. It's a simple, brown satchel that smells of earth. It has 1 load/unit of weight and is made of rustic fabric. The Wonderbag is essentially a small garden; prepared in advanced and capable of being carried on the go. When it is opened, a huge number of shoots, stalks, stems, twigs, and branches come out, these plants allow for easy access in, with dirt at the bottom of the bag spatially warped to be small and lightweight. The garden has the growing space and potential of a small 3 by 6 foot plot of land; it can grow a small number of useful reagents for potions, food items, herbs for sale or taste, and so on. It can be seeded with multiple of the same plant, or several different plants to allow for a wider range. It absorbs sunlight through its skin, so as long as it is outside and being carried on your waist it is gathering energy for the plants within.
 Loamsplit. This is a shovel, basically. It has a translucent head which vibrates slightly when jostled or touched. The power of this item is that it can shear through most materials to dig a small impression in the dirt. Invaluable in dimensions with endless metal floors or solid soil for digging latrines or uprooting crystal plants. This item has a similar level of cutting ability and hardness as adamantine, but without any bonus to attack if used as an improvised weapon. It also requires daily maintenance in the form of covering its blade and face with oil. Finding a Loamsplit also requires finding a source of this oil; average expeditions can only scrounge up 2d4 weeks worth.
Explorer's Companion Table – Roll 1d6
 Astral Cats. Astral Cats look like normal cats, except with a starry colored fur like the night sky. Different breeds have different constellations, and these comfortable familiars are invaluable for their ability to hunt and kill astral parasites. They also seemingly work in any dimension, able to perceive both the physical plane and the astral plane at the same time, a trait partially shared by their more mundane counterparts.
 Energy Snakes. These almost always appear in the physical realm as made of metal, stone, or even drawn on paper. The Energy Snake lives 90% in the Astral Plane, and is a filter feeder that has evolved to take on the appearance of a snake to survive. Due to how little they need their physical body, they can change it into various forms such as statues or ornaments, as well as changing sizes, though the creature will still die if this body is destroyed. Anchored to one point, they simply drink the pathos and ambient energies of the Astral plane; they are not a pest and are in fact useful to see the “winds” of the astral plane at any given time by observing their astral body, tethered to their physical body and whipping against any strong astral gusts signifying great events or the birth of great people.
 Spirit Valets. These servants and assistants work for the Celestial Bureaucracy. Their primary job is to keep reality running, and to deliver messages between the angels and constructs in abstract and hidden places. However, there are so many of them that there is little overhead; and almost all of them are treacherously corrupt! They work for high level characters in the hopes of earning a high amount of treasure, magic items, a pocket realm carved free from its monsterous owners and so on- in exchange they bring an air of semi-legality to everything the adventurers do in the outer realms and help produce the warrants and tickets needed to keep you from getting thrown into a prison made of stardust by celestial enforcers that wander the void between spaces. If you really get on its good side it will help your soul return to your home dimension so you can enter your rightful afterlife or be revived; if you were a bad and abusive employer then the Spirit Valet will make sure you don't find your way back.
 Lil' Moon. Many dimensions have skies, and many worlds have moons. The small floating discs, suspended in the night sky. However many worlds have become dead and silent, or been destroyed utterly, leaving the moons with nothing to do. These tiny moons travel between the void of space and between realities, sometimes joining people on their journeys. While they lack most physical presence, these moons can influence things based on the powers attributed to moons; suppression of lycanthropic power, manipulation of tides, influencing disease, control over a woman's menstrual cycle, flowing or stilling of waters from the tides, and many other small but useful features. Moons typically just want to watch interesting things, and their power and intelligence wanes and waxes with their phases.
 Loyal Locale. The extra dimensional spaces belonging to certain Wizard's in their spells, the rope trick, the tiny hut, the magician's outhouse, all function as having a secondary “place” that exists outside the main reality. However, after years of being forgotten or casted incorrectly by a bumbling sorcerer these spaces are more alive then ever. Capable of following people they like or called upon by new souls- these places may offer respite to weary travelers between dimensions. Unlike the normal version of these spaces that are obedient spells; these places are alive and very much active. They may superimpose themselves over a room you are in, their varnished floorboards subtly pooling in over the cold stone of the dungeon, or they may become hesitant to let certain people or objects leave their space into a full, proper dimension too soon. If the original Wizard who created the spell loved the color blue, then this space may very well be colored blue, and won't let anything blue back out of it once given without a fight or unless you have a very good reason for it and promise to return it right away. Be warned; making a 'place' angry makes a powerful foe.
 Frozen Soul. As each and every moment passes in time, the eventual fate of each world and universe freezing in utter darkness becomes more and more certain. In these many worlds; the souls of timeless lost people are frozen in time until, eventually, their crystallized consciousness spreads out of their dimension and into a new one, giving it just enough warmth to regain itself and fly again as a specter. These Frozen Souls are wise, generally helpful beings who have spent soft eternities staring at nothing and contemplating reality. Extremely useful for any time distortions; this spirit will gladly sit in a single spot for a thousand years of boredom just to tell their friends what transpired outside this dimension; where time moves at a breakneck pace. In dimensions where combat may be needed; the Frozen Souls can channel the power of their ice into chilling armor for allies or deathly freezing touches to monsters and other foes.