It's more of a kids activity, but it's still a fun way to kill time. You have to download a app on your phone, I just searching "geocaching" and found one. The cache is usually some small container, there's nothing of value in it but you can put your name inside. It's a great way to kill time with your kids or if you are in an area and have some time to waste. The app shows you a location nearby and you follow it on your phone, there's no direct directions, just a line from your location to the cache.
Think of it as a kind of scavenger hunt, the fun is in the searching. It took me about an hour to find one in the park by our house, my kid was super excited to see it. I'd highly recommend this especially for parents of kids about 4 years old and up.