Things About Dungeons I

There are many types of dungeon environments, and each has its unique features that the GM can use in descriptions, or exploit when challenging the adventurers.

The simplest dungeon construction is an excavation or earthen construct. The walls are packed earth, the spaces are small and cramped to prevent collapse. Timbers, supports, or plant roots can keep moderately larger spaces intact. Any kind of digging into the walls gives a 5+ chance on 1d6 of causing a collapse, and any collapse can trigger a collapse in an adjacent area, possibly creating a cascade of collapses.

Small quantities of dirt will sift downwards from the ceiling, constantly. It might not be enough to be annoying, but everyone will definitely be grimy when they leave the excavation.

Water above, such as rain soaking into the ground, will seep into the walls, potentially weakening the tunnels. Damp earthen walls should scare delvers.

If there aren't any timbers or supports, the excavation is probably being used as a burrow. Expect surface animals. Burrows rarely go deep.

Small artificial excavations are probably storage of some kind, like a root cellar or burial chamber. Larger excavations tend to be tunnels rather than rooms, and are either mines or passageways to another location.