The kettlebell is a cast iron weight with a handle attached. It looks very much like a cannonball and can be used not only as a strength training device, but is also excellent for cardiovascular exercise. They come in many sizes and colors but the shape is typically the same – round. I prefer a plain black kettlebell with no special features such as vinyl coating or a rubber handle.
There are a variety of exercises that can be done with the kettlebell. My personal favorite is the two handed kettlebell swing. It’s an excellent place to begin. Here is a great instructional video by Kettlebell Queen Lauren Brooks. Many of the exercises can engage the entire body at once, making it not only a fast workout, but a highly effective one.
As of today (10/25/2012) I have been unable to find a good source for calculating calories burned with a kettlebell. If you come across one, please let me know!