One of my biggest and most complex maps, played twice at NTRPGCON. Erol Otus played in the first adventure. Beware of CHARLIE.
Here is the map of the Greyhawk catacombs and sewers. It's probably one of my favorite dungeon maps. A river runs through these sewers, along with stairways that descend 1,600 feet. And how could I fail to mention the immense underground lake, complete with an island and a boat?