It doesn't happen often, but sometimes at work I just start to doodle, and sometimes I draw dungeon maps.
This first one is obviously on a post-it. It's a natural cave that slopes down to a chamber with an underground river. At the back of the chamber is a stone door, leading to a worked corridor. Going left takes you even further down into a set of linked rooms. Going right brings you to a semicircular chamber.
This dungeon is also dug into the side of a hill/mountain, but is completely worked. Along the right there is a large chamber with multiple deep alcoves, and a raised area at the back. Down at the bottom is a chamber dominated by a large statue. Prior to that chamber is a small hidden room. Further to the right, is a very very long corridor leading to a pair of rooms. So long I didn't bother drawing the whole thing, but I'm thinking probably a mile or two long, and sloping very gently down. Before that is a side branch with a pillared chamber with several smaller adjoining rooms.