Try a beginner's dance/acting thing. It'll be physical, but not so much that you'll be totally out of your depth, and everyone there will be as awful as you might be, what with it being "beginner's". Plus, you'll meet lots of new people - and if you don't like it, it's not so huge a commitment?
This next one's only definite for UKers (it most likely exists everywhere elsewhere, but I don't know for sure): join a fun-hiking group. Similar to dance: lots of people, physical, but not super-taxing. Plus, pretty scenery?!