|A snippet of atypical Delorme Atlas page|
Delorme is a map company. Among other things (GPSs etc) they publish paper atlases, including one per state in the US. The Delorme challenges require a cacher to claim finds for all pages in a given state. Once that happens, they are given access to the coordinates for the final cache. Once that log is signed, the challenge is completed.
To give you an idea of the scope of the challenge, here are some stats for the North Carolina challenge: Each full page covers 24.6 x 35.5 miles, tho some "pages" are smaller than that. There are 78 pages covering the state of North Carolina, 77 of which are required to complete the challenge (the other one doesn't have any caches in it, so its a freebie). To claim a page one needs to find any cache except event caches. Caches found previously to accepting the challenge also count towards pages, so odds are you already have some pages claimed and didn't even know it yet.
These caches are a great way to explore your own home state, and I highly recommend trying the challenge in your state. A complete list of challenges is here.
Go forth and explore!