You find dungeon features in the dungeon. These can be doors, doorways, fountains, staircases, traps, water, ..., and if you ever find it, the drawbridge.

Dungeon levels (like that of The Oracle) and dungeon branches (like the Gnomish Mines) have subcategories here, Category:Dungeon levels and Category:Dungeon branches.

The dungeon features also include rooms, especially special rooms. Rooms might need their own category later.