I recently watched the stop-motion psychological horror film Mad God. It was pretty cool, though a little too impenetrable for my liking. However, the film itself isn't what I want to talk about today.
The beginning of the film has this great shot of the main character (the Assassin) going down a suspended elevator/diving bell down multiple layers upon layers of underworld- past a giant prison with cannons shooting at him, trees in a dark forest, underground caves with fossils and giant skulls, and gardens of giant statues. As we go down, we get a sense of the immense scale and depth of this place. Something about it really reminded me of a massive dungeon crawl- a megadungeon's possible depth- but with a caveat. Exploring a megadungeon is a slow and laborious process; but the Assassin in the film is moving past layer after layer quickly, almost conveniently. To me the feeling was less of just bypassing all this interesting stuff, but more that these levels or layers of the dungeon had already been conquered before. This gave me an idea for megadungeon exploration in the long, LONG term, and a little narrative trick.
The Descent
Each floor of the dungeon is kind of like its own separate place. Of course, dungeon floors can be restocked with monsters and encounters over time- but these give very little reward compared to the treasures found. Once looted, treasure does not simply materialize out of thin air- so you have to crawl ever deeper to get more loot. What this also means is on repeat visits, you will have to travel through still dangerous and restocked floors to get to the deepest and more lucrative parts of the dungeon- meaning leaving and returning without full bags and without expended resources is inefficient and potentially deadly.
But as you explore deeper, this problems gets worse and worse, until the trip down can become as draining on your resources as the actual dangers of the deepest floors. Unless you're cheating the journey down, even a fully cleared dungeon floor still has a few still active traps, hazards, or random encounters which could slow down or expend your party's resources. How do you manage this?
Simple- you carve a big hole, and you build a shortcut.
Most fantasy dungeon crawling games assume a roughly medieval level of technology- where such a construction project is much less feasible. It's not totally unheard of; large pulleys and construction cranes, both animal and man powered, were a thing in those times- simply expensive and not surviving well into the future. I don't claim to be a historical expert on this subject, but it certainly seems doable. Regardless of how realistic it is, for the purposes of gameplay and the fantasy vibe, we can assume a non-magical descending platform can be built at the site of the dungeon.
In order to build this elevator, the party must first secure the top and then hire experts and workers to build it. The total cost of the elevator is equal to the total treasure found on the deepest floor the elevator can descend to + 2. Meaning if you want to build a shortcut to floor 4, then you'd need about all the treasure you can get on floor 6. In typical oldschool megadungeon fashion- each floor of the dungeon has enough treasure to level up a party of the same level once, and exp doubles each level. Roughly speaking, you'd need all the treasure on floor 6, or half the treasure on floor 7, to build an elevator to floor 4. It's expensive, but the cost of building the elevator still counts for the purposes of XP- if we're using gold per xp for treasure recovered. This means the entire party can chip in.
On repeat visits to the dungeon; you can use this elevator instead. The cost of the elevator is much higher then you would assume because of the cost of excavating the material, keeping it clear from monsters of the lowest depths, hiring the skilled (and trusthworthy) operators who won't drop you into the chasm at lethal speeds, and so on. And the other catch? You can't go back up with the elevator, it only goes down. As such, you can't actually use this to carry back all of your treasure you found, but you can shortcut some of the resource sinks of the upper floors. This also becomes somewhat unnecessary when you consider the Jayquaying of the dungeon, with other paths in besides the main entrance or shortcuts to deeper levels, but having a very reliable entrance that you can't be attacked in or taken from you would still be worth the heavy gold investment building one of these would take.
Whenever you travel down the elevator, you will see a cut through each floor of the dungeon. Unless you're autistic enough to mark an exact vertical slice of the dungeon in 3d space and determine exactly what rooms and passages the elevator would travel down through, I would just state a general look for each floor you pass through and use that. If the crypts and catacombs were level 1, then the first floor you pass by you'd see bones and tombstones poking out, some almost seeming to try and reach the elevator occupants. Floor two was the spider's nest, so webs and desiccated bodies are visible down the elevator shaft here. Floor three was the mushroom forest, so thick spores fill the shaft as you go down further and further. While veteran party members will remember each floor, conquering them one at a time, new party members will get to see a snapshot at the dungeon's history and the painstaking effort it took to map and slowly explore each level of the dungeon. Essentially, you would describe the most notable features of each floor as a sort of treat and reward to show how far you've come, before the platform reaches and deeper floor. While it does bypass a lot of the trouble of the upper floors, the gold cost calculated based on floor depth means you can't go right back to the richest part of the dungeons with each visit, and would still need to do some local navigation before getting back to where you were- it's simply much more efficient then walking down from the top floors all the way down again.
Side note- I also really like the idea of the elevator being able to go back up, but only at the exact weight designed for the party on the descent. This means the party can make a hasty faster retreat up the elevator if they can't survive the upper floors, but they can't bring any treasure. Unless a few of them didn't make it...