I’m terrible at drawing maps, and designing rational floor plans. Sometimes I’ll Google image search (GIS) things like crypts or temples, which is always turns up tons of great stuff. Like this Egyptian temple:
and this plan of Olympia:
Or this abbey:
But sometihng you might overlook are other types of plans, particularly those for old gardens. If you GIS “garden plans” (or better yet, “historical garden plans” so you don’t get as many modern drawings that are actually illustrations rather than plans).
The garden a the palace of Versailles is particularly vast and you’ll find lots of images like this map:
or this elevation:
Weird symbolic plans can be inspirational too:
Whether you were planning to run it as an outdoor maze or an underground dungeon, the unusual layouts can help break the monotony of halls and rooms.
Limiting your search line drawings or black & white makes even generic searches for “plans” useful.