One time I built an arena out of kinetic sand, with shaped obstacles and dunes and stuff, then scraped a grid into it for battle. I built some working pit-traps into the sand itself that only collapsed with enough weight was placed on them, and I glued small weights to the bottom of the player minis to trigger the traps, while using light plastic kobold minis for the monsters, which did not trigger them.

The next week my girlfriend responded by running her game with a functioning sewer system with variable water levels.