An infinity pool (also named negative edge or vanishing edge pool) is a swimming pool which produces a visual effect of water extending to the horizon, vanishing, or extending to "infinity". These style pools are often very expensive and can cost up to as much as USD $80,000.Note that the term "infinity pool" is also used to describe a lap pool that has an automated current so a person can exercise by swimming a single infinitely-long lap against the current. This allows exercise pools to be built in small spaces yet still be useful to athletes.

My favorite infinity pools are at Jade Mountain Resort, St. Lucia

http://www.jademountainstlucia.com/infinity_pools.html