Desks, an interview room and a holding cell — the cases where the investigation is happening inside the building.
An open-plan floor of desks, meeting rooms with glass walls, an archive, a break room, an evidence store, the interview room. Institutional plans are regular and rectangular, which sounds like it should make them easy and does not: regularity means fewer distinctive rooms to pin a person to.
The open-plan floor is the difficulty. A large undifferentiated room absorbs suspects without telling you much, so these cases push the work onto object clues and traits — who stood by the filing cabinet, who was nowhere near the coffee machine. A good theme for learning to read object clues properly.
A case picks its floor plan from this theme’s room pool, so the same places recur across the drawer and you learn to read them: Open Office, Meeting Room, Reception area, Chief's office, Interrogation room, Holding cell 1, Holding cell 2, Armory, Forensics lab, Evidence room, Locker Room, Break Room, Archive, Briefing room, Garage. No single case uses all of them — the generator and the hand-built cases alike take a subset, which is why two cases in the same setting can still feel unalike.
6 cases — 4 easy, 1 medium, 1 hard, on boards from 6×6 to 8×8. Every one is verified to have a single solution reachable by forward deduction alone, so none of them needs a guess.