- Cluny Abbey: http://www.cultus.hk/talks/global/cluny_plan.html
- Derinkuyu underground city: https://global-geography.org/af/Geography/Asia/Turkey/Pictures/Cappadocia/Schematic_of_Derinkuyu
- Wieliczka Salt Mine: http://travel.nobelplaza.com/country/poland/malopolskie/wieliczka/wieliczka-salt-mine-map-horizontal.jpg
Any relatively sprawling historical place can do. (Image-search for "X plans" and "X photos" where X is your place) You can annotate them with whatever theme you want, look also at real life photos for inspiration. I mean to run something like this at some point. Real life cave systems, on the other hand, are mind boggling.