The Onegeon Manifesto
It has been remarked that 2025 is the Year of Manifestos in TTRPGs, and I'm here to offer one more. In recent discussion on Bluesky about the definition of a Megadungeon started by Josh of His Majesty the Worm fame, a joke from Brad Kerr prompted the insight that, if you were to apply metric measurement prefixes rigorously (e.g., Kilodungeon = 1,000 rooms and Megadungeon = 1,000,000 rooms), the basic unit would be a "Dungeon" consisting of a single room. While designing for a single room seemingly flies in the face of good, coherent, dungeon design, this has inspired me coming off the discussion of Earth and Wine on Between Two Cairns--a dungeon level to be inserted into megadungeons--to think about designing modular dungeon rooms that can be slotted into dungeons as needed. Meriah helpfully provided the term "Onegeon" which I'm using here with permission for this concept.
The Manifesto is simple. Take time to design a dungeon room that is interesting enough on its own to be useable when slotted into a dungeon someone else is designing. Give it a tricky puzzle, a weird little freak living there, an unexpected boss monster, treasure you can find nowhere else, anything you can think of that would make someone want to grab it and throw it into their game as quickly as possible.
Some guidelines for the ideal Onegeon:
Make it system neutral as much as possible, relying on descriptive terms the Referee can interpret for themselves rather than game mechanics to make it work;
Make it small, fitting on one side of a letter-sized sheet of paper at most;
Make it either bland or entirely unique. If the appearance of the room isn't notable, don't describe it, and let the Referee fit it into what they're already doing. If it is notable, go all out and make the description of the room so interesting that it will stand out to players and make them question what it's doing here;
Make it weird. Anyone can think up a room with d4 White Apes in it. make a room that's weird and interesting enough for someone to want to use it.
With that said, I'll also be launching the obligatory Onegeon Jam starting next month and running the rest of the year to give folks a chance to work on these and share what they've done.
As a guide, I'm also including a sample Onegeon below based on a room I've used in a homemade dungeon before.
Which Way Do I Go?
A 100 ft. cube of a room with entrances on opposite walls. Between them is a winding elevated pathway 5 ft. wide and 20 ft. above the floor. The pathway is dimly lit by glowing stones set along the edges, but the spaces above and below are hidden in shadows. Ideally, place this on the way to an important room in the dungeon so that players must take this path to get there.
There is an enchantment that confuses the sense of direction of anyone who walks on the elevated pathway. Each turn, players must use their mental/psychological capacity to overcome the enchantment. If they cannot, they must roll 1d4 and move half their movement in a random direction-1 = North, 2 = East, 3 = South, 4 = West. They will fall off the walkway if forced to move in a direction toward its edge.
In the space below will be at least 8 monsters of a moderate difficulty. I would recommend skeletons or other undead remains of previous adventurers who fell down here and died, but that may be substituted for monsters consistent with the dungeon. They are not inherently hostile, and could be petitioned for help if approached correctly and offered assistance getting out of this pit. There are no ladders or stairs to get out, and players must improvise a way of getting lost party members back up.