Here are a few dungeon map ideas:
- A wizard’s laboratory that is divided into four sections, each section resides in a different elemental plane and are connected to each other via portals.
- A labyrinthine crypt beneath a large hill which has been converted to a base of operations for a band of brigands.
- The crumbling basement complex of an ancient castle which no longer stands.
- An urban evil temple which uses a luxury bathhouse as a front.
- An ancient dwarven hold which was abandoned after the mountain it was built into erupted, flooding sections of the complex in lava.
- A frost giant hall that was carved into an iceberg creating a floating ice palace.
- Illithid U. You would need wotc’s permission to use the name, but the idea is still good. A bizarre underground school / lab where the fine arts of dissecting humanoids and controlling slaves are learned, featuring auditoriums, libraries, labs, jail cells, and living quarters for the teachers and students.