LoL i was going to say something similar to the branding iron thing but...
Have you ever heard of the 11th hour?
its a very old game... but its about a person roaming around a haunted masion trying to solve a mystery by solving a lot of puzzles.
anything using your mind trying to solve hard problems are fun! much better than just point click attack

example of a puzzle: You find yourself in a library. In the middle of the room there is a desk with a note(data disc if you like). It reads "An open mind reads the books that contain useful knowledge that goes round and round".
There is a keypad that takes in 5 digits to unlock the door.
Then you roam around the library looking at the walls. The walls contain missing volumes within the shelves. Then you display the missing volumes to the user. Then you can use that information to solve the 5 digit lock to open the door.
Simple, and if you have the right sounds, you can set a creepy mood...makes me want to make a map now
