San Alfonso del Mar is a private resort in Algarrobo, Chile, about 100 km (62 mi) west of the capital Santiago. The resort is recognised as having the world's largest swimming pool.
The pool is 1 km (0.62 mi) long, covering 8 ha (20 acres), containing some 250,000,000 litres (55,000,000 imp gal; 66,000,000 US gal) of seawater, with a maximum depth of 35 m (115 ft). It uses water pumped, filtered, and treated from the Pacific Ocean.
Watch it on YouTube : WORLD's LARGEST SWIMMING POOL