First, let’s talk about dungeon maps.
A floor of a dungeon is usually represented as a floor plan for a floor of a house. The dungeon map evokes the thought of a level floor with little to no variation. This makes sense because most dungeon maps are built on two-dimensional planes, like a sheet of paper, or a computer screen.
If the dungeon is a building that is in good repair this makes complete sense and the preconception stands. However, when in a cave system this preconception is far from the truth. The floors of caves are rarely level, and if they are it should evoke suspicion from your players.
DM: “The floor is completely flat and smooth.”
Player: “The cave floor is flat and smooth? That’s unusual. I toss a heavy rock onto the smooth section. Does anything happen?”
DM: “The place where the stone hit breaks and the stone goes straight through. After a few seconds, you hear the clang of stone hitting metal.”
Player: “Oh, no! A pit trap with spikes at the bottom!”
Keep this in mind when creating your dungeon. The floor may well be level and smooth throughout the dungeon, depending on where and what your dungeon is.
When making a dungeon map it is difficult, again because we draw in two-dimensions, to show passages going under or over other sections of the map.
You might say: “But wait, Josh, that would be another floor of the dungeon, wouldn’t it?”
Not necessarily. A sloping passage may lead to another level of the dungeon, but if it leads to a room that is on this level of the dungeon, and it must overlap other areas to do so, it can instead be a passage that goes over or under another section. Usually, you would do this to connect two rooms that you want characters to be able to return to without going through all the rooms and corridors between.
If going under or over feels too strange just don’t do it or find another way to link the rooms. In fantasy or sci-fi, a teleporter can link two rooms instead.
Now, non-Euclidian geometry
When using a magic-infused dungeon you can use non-Euclidian geometry. There is no way that the room over there has a door that leads directly to this room here, but for some reason it does.
In a setting where you can mess with gravity (such as with the reverse gravity spell or gravity generators), a circular corridor may use a Mobius strip to allow people to visit two floors without using stairs or other classic ways of changing floors. This allows characters to walk from a point and eventually end up where they started, facing the same direction. Let this confuse the players. Don’t tell them that this is a Mobius strip, let them try to piece it together for themselves.
Next, let’s talk a little about getting from floor to floor.
In the Dungeons and Dragons 5e Dungeon Master’s Guide in the random dungeons appendix the list of things it has for “stairs” include stairs, chimneys, and elevators (or empty elevator shafts). Chimneys can be reskinned for your dungeon of course. Underground this may be a tunnel, for example. Elevators don’t have to be a room that rises and falls from floor to floor, it could be a basket for one medium sized character at a time.
Here are a few things that are dungeon features for getting from floor to floor that aren’t listed in this appendix in the 5e DMG.
One option, as mentioned earlier, is teleporters. This can be a pair of linked two-way teleporters, a one-way teleporter, a teleporter system that works in sequence (teleporter A takes you to teleporter B, B takes you to C, C takes you to A), or even a random teleporter with multiple teleporters linked together. These can be fun and confusing to your party.
Sloping floors are another interesting way to get from floor to floor. Maybe the corridor slopes so slowly that the characters believe they are on the same level by the time they get to a room or the slopes are obvious, and the characters know they have changed floors.
A combination of shafts and sloping floors can be a chute that a character can go down but can’t get back up. This allows for one-way movement or even separating the party if the chute is under a trap door.
Living elevators. A living elevator is a creature that moves you from one level to another. This can be a mount that only moves you between floors, but it can also be something more…unusual. In a magic dungeon, this could akin to being swallowed by a living elevator shaft to go down. Going down could be strange but going back up would be…vomitus.
Ladders. I mentioned chutes earlier, and I would be remiss not to mention ladders. Like stairs, these are a more mundane way of getting between floors, but they require you to go one at a time. Or if the ladder isn’t bolted close to a wall you could manage two at a time. Being attacked while going up or down ladders is a great way to get the players separated while they are physically right next to each other. The wizard is right there, but he has to get to the end of the ladder, so his hands are free to cast his spell.