It's a high intensity workout that combines cardio, weight resistance, and competition with yourself. You can do the workouts on your own, but I'm in love with this group that does it in a big industrial garage that they've converted into a gym. They call it The Box, and it's filled with kettle bells, jump boxes, pull-up bars, and mats. Basically, you go in and your coach gives you a series of movements to do i.e. squats, push-ups, sit-ups. Then you do it as hard and as fast as you can for as many rounds as you can. The routine changes every day because the variety builds total body fitness. A key component is that you track your progress and compete with yourself. It's really hard to explain what it is. Check out this website if you want to learn more: www.Crossfit.com.
Anyway, The Box feels like an old-timey (I can't believe I just used that phrase) boxing gym. It's just a bunch of friends hanging out, working on whatever skills they need to work on, helping each other out, and providing lots and lots of encouragement. I went to a group session yesterday where we divided up into teams and competed with each other. The series was hard and it kicked my ass. But it was the most fun I've had in years. It was absolutely the ONLY time I've ever had fun while working out. I'm totally hooked even though I feel like I was hit by a car today.
Oh yeah, and I've got my first race this afternoon.