At the San Alfonso del Mar resort in Algarrobo, Chile, you will find the largest swimming pool in the world. The pool is .62 miles long with a maximum depth of 115 feet and contains 66 million gallons of seawater. Water from the Pacific Ocean is pumped, filtered, and treated in the pool. It took five years to complete the project, which was completed in 2006. Construction cost estimates range from $1.5 to $2 billion for the behemoth and an additional $4 million per year for maintenance.
Source: Odd Stuff Magazine