Foamboard, PVC pipe and fittings, and various accessories from toy lines. And lots of hot glue and paint.

Here's the Resident Evil playset I made (I say playset instead of Dio, since this as logged about 6-7 hours with my kids already).
This is from the Code Veronica game- the boiler room from the military training facility.

This set is 20" X 30" This is something I've wanted to make for a while now. Altogether this project took me about three weeks to complete. Mostly because I had to wait on parts to finish it.