Free - iOS / Android
Did you ever wanted to hunt treasures ? This app is for you ! It's the official application of geocaching.com with over 2,5 million active caches worldwide.
At anytime, you can start an adventure by touching the "find nearby caches" button or share your discoveries with members of the geocaching community.
Geocaching is a good way to add a fun side to hiking or biking activities.
Even if it's the reference, there is a lot of apps for geocaching, just search for "geocaching" in the Apple Store or on Google Play.