This is the longest swimming pool in the world located in off a coast in Chile. The length is about 1km long, has a 35m deep end, and holds 250 million litres of water.
The waters are so crystal clear that you can see the bottom even in the deep end area. Staying in this hotels will not comes cheap thou. With the cost of building this pool at 1 billion USD, and the annual maintenance of this pool at 2 million.