About Acadia's EarthCache ...
My family did the multi-cache program at Acadia this past spring and thought it was really well done. The caches were EarthCache's and you had to solve the riddle to get to the first one then find the clue to find the next (which involved solving another riddle on the clue to find the next one -- and no hidden 'boxes' were involved).

It was a very clever program and after finding all the EarthCaches, the last riddle brought you to a place where there was a letterbox-type stamp to complete the program (we were glad we had our letterbox notebook with us for that). The kids were also happy to have the password for the website they have set up for this EarthCache to print out their 'official' park certificates for completing the program.

It took about 5 hours total to do the EarthCache program at the park (driving time to find each EarthCache because they are all over the park and require some hiking as well). We thought it was well worth the effort to spend the time and learn all kinds of interesting features about the park.