Today I just went out and did my first geocache for 7 years (hiatus mostly caused by arrival of the wee one, he came with me today though - with “his” GPS - aka my old one).
When I did the first one a little over 8 years ago there were precisely 5 (five, count 'em) geocaches in the UK, and I drove 120 miles to do it (well not just for that) - now there are apparently 100 or so within cycling distance 
Gets you out and about with the GPS often to little trodden footpaths - which of course you can get home and map 
So other than plain ol’ walking and cycling - what else is there?
There’s Geograph - but like the map of the globe at the end of the 19th century, the blanks spaces are few and far between…
I seem to recall that there was a “game” involving a 60 x 60 grid based on latitude/longitude and 2 “teams” would compete to own the squares based on marking and photographing aa° bb’ N/S cc° dd’ E/W where the aa/cc was discarded and the bb,dd was the important part… no idea what the game was called though 
Anyone got any other “games” to play? 