New kid on the (services) block: geocaching is on the Locify now! With all geocaching features you can expect: listing of nearest caches, navigation to the cache, downloading full listing or decrypting hints as main ones. You can even save caches on your phone and hunt for them in the terrain without the need for data connection. If you are not geomuggle maybe it is worth of give it a try!
And if you are geochacher and geocoder, you can review and download the code behind and enhance or use it on your server. Read more about geocaching service implementation with full PHP code.