Officially the world’s largest swimming pool, San Alfonso Del Mar cost $2 billion dollars to build. Located on the beach front, the pool uses technology developed by the builder, Crystal Lagoons, which filters and pumps the nearby ocean water into the pool. This means they don’t have to pay for the water to fill the pool, which is good because it’s 1 kilometer long and holds 66 million gallons of water! This pool is large enough to sail a small boat in and is connected with a resort and condominium complex.