Barrowlight.

PROCEDURAL GENERATION

Floors built
from modules.

Each floor is a 3×3 grid of cells that fit together like tiles: hand-made set pieces mixed with rooms generated on the spot.

Every cell has the same footprint and the same four doorways, so any cell can sit next to any other. A random spanning tree joins the grid, which guarantees the whole floor is connected, and most of the remaining doorways are opened too, so there is usually more than one route and monsters can arrive from more than one side.

So that no two floors share an outline, up to two cells are left as solid rock (an L, a U, a ring, never a floor cut in two), pairs of cells merge into big rooms such as a nave or a rift gallery, and doorways slide along their edges. Some rooms hold chasms: a well-timed shove drops a foe to the floor below.

About half the ordinary rooms are generated: pillared halls, rooms with several doorways, ruins, or cellular-automaton caverns, built around wherever their doorways fell. They must pass the same validator as the 28 hand-made rooms, so a generated room can never cut off a doorway. Landmark events, a boss arena or a sealed vault claim their own cells, and furniture is placed in whole arrangements, kept only if a flood fill shows nothing was cut off.

Some rooms bring their own fight. In the Rift Crossing, guards hold both bridges and archers fire from the far ledges; a guard never leaves its post, so you break through or knock it into the rift. In the Gauntlet, ambushers wait hidden in the side rooms and step out behind you, but revealing themselves costs their turn, so the ambush is felt but fair.