Kettlebells—iron-shaped balls of varying weights that, with their affixed handles, resemble carry-on cannonballs—provide a low-impact total body workout that simultaneously increases strength and stamina. A recent study found kettlebells to be highly effective, resulting in subjects burning "at least 20.2 calories per minute, which is off the charts. That’s equivalent to running a 6-minute mile pace." You'll learn all this and more during your intro to kettlebells class (which you can apply this Groupon toward). Upon completion, you're free to take more kettlebell classes (drop-in classes are $16) and Pilates mat ($12.50–$16) and apparatus sessions (private session are $54–$60, duet sessions are $37–$44, and semi-private sessions are $30–$38). Feel free to combine these classes at your whimsy to transform yourself into a formidable fat-burning, cardiovascular-boosting, muscle-building monster without the assistance of a full moon.