Dungeons
A dungeon crawl doesn't have to sit underground; ruins reclaimed by forest roots or sunk into swamp bog share the doors-and-walls toolkit.
Parent page Underground
Dungeon environments, which include both ruins and contemporary buildings constructed in the wilderness, are a fairly common venue for adventures. As an environment, they combine urban features like doors and buildings (page 92) with features from an underground environment, and occasionally components from other environments. While underground dungeons are particularly common, you might also consider setting your adventure in a ruin reclaimed by the forest, with giant trees spreading their roots through the walls, or a ruin deep in a swamp, with bogs covering access to some of the ruin’s hidden secrets.