There is a computer game, Escape Simulator, that has a ton of user generated levels. You could check out some LP's on youtube of it, see what players think of certain rooms and the puzzles in them. Yes, a fair amount boils down to finding a combination but I've seen some pretty creative uses of how you get the numbers. Obviously there are things you can't do in the real world, but it might spark something you like when it comes to hiding clues in plain sight.
The ball is round, the game lasts 90 minutes. That's fact.
Everything else, is theory.