In urban areas, sometimes in addition to geocaching, there is "letterboxing" which is closely related, but depends more on following a patrol map using riddles.

My DD11 loves letterboxing.

There are also a lot of 'geek-science' books out there now that describe all sorts of very cool home-made contraptions to make out of pretty cheap/recycled supplies.


Schrödinger's cat walks into a bar. And doesn't.