San Alfonso del Mar is a private resort located in Algarrobo, Chile, about 100 km (60 mi) west of the capital Santiago. It is notable for having the Guinness world record for the largest swimming pool in the world. It has been attracting tourists since it opened in December 2006.
San Alfonso's pool is one kilometer, or about 3/5's of a mile long. The pool covers an area of 19 acres that holds 66 million gallons of seawater. The pool, developed by Chilean company Crystal Lagoons, uses water pumped, filtered, and treated from the Pacific Ocean to supply to the pool.