Orienteering
I’m a little surprised it’s taken me this long to hear about geocaching, especially since there are many people here who enjoy bushwalking. Essentially, you head off into the (semi-)wilderness and leave stuff behind for others to search for, sometimes including a tracking device meant to be reused in another cache elsewhere. There are also “event” caches, but if there’s no party when you get there, I suppose it’s because you were late. Or early. Because you need a GPS device, this is probably a long way from taking off. (It also reminds me of all those people in the 1990’s searching the continental U.S. for druidic runes.)