Swim at SAN ALFONSO del MAR, Chile

World's Largest Outdoor Pool At Chile's San Alfonso del Mar Resort
The largest swimming pool in the world is more than 3000 feet long, with a deep end that descends 115 feet. Sitting seaside at a resort in Chile, the pool required nearly five years to build and cost $1.6 billion. It has an annual maintenance fee of $3.2 million. Containing more than 66 million gallons of water, it dwarfs the second biggest pool in the world (the Orthlieb in Morocco with a mere 9.5 million gallons). The pool keeps a constant flow of fresh seawater into the pool and old water back out to the sea, using a filtration system to desalinate the seawater before it goes into the pool and clean the pool water before it goes back to the ocean.
Source: popularmechanics.com