The Climbing Block levels and stabilizes your front wheel as you do a workout on your indoor trainer. What's unique about the Climbing Block, though, is that you can rotate it to set your wheel higher than your trainer, thereby increasing the level of difficulty of your workout. The goal here, of course, is to more accurately simulate climbing. You can rotate the climbing block in any of three positions to increase the steepness of your "climb", you can also purchase two Climbing Blocks and stack them on top of each other if you'd like to replicate climbing the really steep Manayunk Wall and Kemmelberg-type stuff. With the use of two blocks, you'll end up with 9 different levels of steepness to choose from. The injection molded construction is virtually indestructible. You can count on many long winter nights in front of the TV riding like a madman thanks to its superb durability.