Gnome Laboratory, Workshop, and Planar Observatory (3 lvls)
I made this for a 5e game. In my campaign, the observatory's mission is to spy on the denizens of other planes, research the planes, and to use newfound knowledge to protect the material plane from would-be invaders. The director is a brilliant gnome who has created automatons and clones to help him run the place. He's a bit of an ends justify the means type.
The west wing of the main floor houses a kitchen, the director's quarters, and a common area that includes a library and dining area. The east wing includes a courtyard and a large room that hides a menagerie of beings from other planes for study. Access to the basement is also in the east wing. The basement has different types of cells to detain different types of planar beings. The second story, accessed by stairs in the west wing, includes a ballroom that was repurposed into a workshop, additional living quarters, and the main lab, machinery, and planar observatory.