Well, this year I started to go to gym. One of the things that I do is "spinning". Spinning here refers to doing a group cycling exercise programme. Normally this is conducted by a trainer using various musical tracks.
In the photo below, you can see that my spinning class is about to start. My trainer, Mr. Chandra, is a certified fitness trainer, a.k.a. "ironman", employed by National Sports Council (according to him), to train our Olympians bound for Beijing.
In an hour of this spinning programme, you can burn up to 800 kilo calories. Also your heart will operate up to 85% to 90% maximum heart rate. This can be achieved by cycling in different body/hand positions, varying resistant and speed.
I can tell you this: this is a real and complete workout. If you are aiming to lose weight or work on your heart muscles, this is definitely recommended.