I've been developing an ecocache challenge that gives GPS coordinates to different areas around our city that are specific to some science subject, like a visible fault, geological feature etc. The subject section of the coordinate page describes the actual science detail the finder is looking at. So far I've been able to include ecology, geology, oceanography and botany into the project. I'm trying to get 20 locations in the challenge to make it interesting and expand the breadth of science subjects.