This dungeon map continues from the stairway of Area 11 of the "Level 3A" map (Dungeon-045.jpg):



This map was inspired by the Ueno-Asakusa line of the Tokyo Subway system. The blue represents water. I envision the pit trap in Area 21 to be a collapsing bridge trap or perhaps a covered pit trap that locks the victim inside and then floods. The dotted line between rooms 17 & 18 represents an illusionary wall.