For #dungeon23 I am going to do an undercity. There’s nothing too original about this of course—the (mega)dungeon under the city is something of a trope of dnd. The implicit setting will be modern/post apocalyptic, but I don’t have interest in developing that for now, I just want to do the room a day thing. I’ll get into thematic inspirations in a separate post, but I wanted to share how I’ll be attempting to map my undercity. I drew ideas from a couple sources:
Hill Canton’s - Pointcrawling Sigil’s Undercity. In this (classic?) series of posts about pointcrawling, Chris Kutalik deals with the challenge of trying to create a truly vast space, one that can’t be reasonably mapped in 5’ square increments (any more that an entire above-ground city could be mapped to that level of detail). That said, pointcrawling also works for Sigil’s “mythic underworld” type undercity, as spaces can be connected by portals or warped space.
This Web DM episode about traveling around the planes, specifically the Infinite Staircase, one of my favorite aspects of Planescape. I was of a mind, in fact, to do an infinite staircase megadungeon with a bunch of planar locations. In that video, Jim Davis makes a somewhat off-handed remark about the map for an infinite staircase campaign resembling a flowchart or subway map.
So, I want to do a point crawl dungeon, with the points being 52 7-room dungeons/locations. Pointcrawls work well for overland travel, where you can overlay the points and paths onto a traditional map (just like you might overlay hexes onto a map). And they should work reasonably well for exploring a large underground complex, like mines or a series of caverns, especially where the characters might not have an easy intuitive sense for how the spaces fit together.
However, a pointcrawl map can produced a map with a warped sense of space (e.g. where two locations seem close but are not). This is especially true when you are trying to represent both horizontal and vertical space. Kutalik addresses this problem by making a point-based sideview map; however, I don’t really see what this adds to a traditional sideview map aside from just being easier to draw.
Putting the above together, it strikes me that designing a pointcrawl map that expresses both horizontal and vertical connections is a solved problem, in a sense: The metro map! Or subway, tube, underground, etc. Take a look at London’s underground map:
I’m imagining that each line (identified by color) can be a different layer of the dungeon. Connection between underground lines can represent spaces where multiple layers connect. Using a metro map for a dungeon in this way would mean that, horizontally, your dungeon layers are more simplistic, often more or less a straight line. But the vertical space is thoroughly Jacquaysed. Imagine a party trying to get from Green Park to Holborn, both on the Piccadilly line (dark blue). They could just travel along the Piccadilly line, but perhaps they want to avoid the faction at the Leicester Square location. So they drop down one level to the Victoria line (light blue) to go to the Oxford Circus location, then drop down, say, six levels to the central line to go all the way to Holborn. But! at the Tottenham Court Road location they discover a huge pit that takes them down to the yet-undiscovered Northern Line, another 4 levels deeper. Do they come back to explore that layer? Will it reveal other connections between locations that could make their life easier?
Underground maps are also useful for expressing undercity connections because they literally traverse and connect the entire city. There’s even space for a river or other water features that one can place below ground instead above. An actual metro system isn’t miles and miles deep, of course, but this where we are megadungeoning the metro map.
But isn’t that too many locations? Yes. My plan is for the connecting points to be fully developed locations (i.e. 7-room-ish weekly dungeons). “Locations” on a map that don’t connect to other lines could be places to roll a random encounter. This might also lead to a decision point for players: do they take the level 3 line that has a ton of random encounters, or do they take an alternate path that involves vertical travel but with fewer encounters?
More metro maps. Imagine these as megadungeons!
I've wanted to do something similar. I live in NYC, and I used to live in Tokyo, so I've been looking at these maps everyday for my whole adult life and they've always stuck me as having big dungeon potential but I've never quite put pen to paper and written a subway-dungeon.
Eager to see your progress and how it works out!