Heart-pounding? Check. Butt-kicking? Check. Totally hard-core? Check. That's what you'll feel when you workout at Fairtex, San Francisco's premier Muay Thai boxing gym. Located in Yerba Buena, this lauded facility has some of the best Thai boxers and trainers around which guarantees you a non-watered down version of cardio kickboxing. Begin your hour-long class (they have intro slots for newbies) by jumping rope for 15 minutes to a soundtrack of Jay-Z that blasts through the newly renovated warehouse space. After a few sessions we were skipping rope like a champ. With around 45 minutes left, you'll segue into pad work where you'll kick, knee, and throw left-hooks and elbows with your partner and an assigned trainer. After a lot of heavy-bag work and a sufficient amount of huffing, puffing, and sweating, you and your classmates are subject to a series of old-school calisthenics that includes real sit-ups (crunches are for sissies), push-ups, and medicine ball work. What will this seeming punishment do for you? We'll tell you; you'll be ripped, in the most excellent cardiovascular shape of your life, burn calories and gain lean muscle mass, and most of all, leave with loads of cool, calm discipline. Despite the sore calves and minor whimpering, we've been addicted since day one.