That's very cool! You've got me thinking of running it as well now. An investigation game needs a good twist, and hiding the treasure like that is excellent.
For myself, I have used a few weird things for dungeon layouts. The best I've actually run was a villain lairing in an old zinc smelting plant -- lots of chimney passages, and a safety interlock-based puzzle.
I've also drawn one based on a Minecraft house (tree farm, nether portal, etc.), and a bandit cave laid out like a diagram of the inner ear. I'm also thinking of using an computer chip layout as a dungeon - one day...