I have grown to love spinning - it's a very intense workout, and it's great for slimming your legs. I'd read that a long time ago, and it's really true. I do it 3 times a week. To simplify it, it's a simulated bike ride - the instructor prompts you on hill climbs (seated & standing), flat road rides - again, seated & standing - sprints, intervals, etc. It's suggested that you allow 6 weeks to build your "aerobic base," so you can work at more advanced levels. I'm a certified spinning intructor through the Johnny G folks, Mad Dog Athletics. I prefer to use aerobic music for my classes, not the suggested "spinning" music like they sell on there site. There are some good DVD's out there to use, too, if you can't make a class.