I started out going to group fitness classes when I was 16. I love them. I still go to the same gym and just about everyone there knows me.
Once you're a regular you really build up a little family

great way to stay accountable too! They question you if you disappear!
Happens to me whenever I'm off (I'm a teacher, so when the kids have breaks..) and I go in the morning instead of the evening. The evening people yell at me when I come back!