so glad you asked. geocaching is a worldwide treasure hunt that anyone can join in on! the game began in may 2000. it's an outdoor location-based orienteering game focused on using gps to locate caches hidden all over the place. caches vary from a micro tube with a logbook in it, to major containers full of items to swap. some are hidden in plain site, some require hikes, and some require puzzles to open, but all caches have the same end goal: find it, log it, sign the logbook, and put it back.
there's a few other aspects to it as well - swaps, for one, are items you can place in a cache and trade for another. my favourite is trackable items, or tracker bugs (TBs). these guys are an item with a code on it and sent out in the world with a goal in mind, and their progress is tracked every time a geocacher moves it to a new cache!
it's loads of fun, and there's caches all over the place - from the cities to the dead wilderness, if you check out the site or the app, you're bound to find something! you can read more about it on the site linked in the sidebar :)