Crystal Lagoons at the San Alfonso del Mar resort in Chile is the world’s largest outdoor pool with more than three fifths of a mile in length, that’s 20 Olympic-size swimming pools.

The enormous man-made lagoon is set halfway up the country’s Pacific coast, in the city of Algarrobo, and is filled with 66 million gallons of crystal clear seawater.

It also hold the Guinness record for the world’s deepest – so if you don’t feel like diving 115 ft to the bottom, it might be best to bring some spare goggles.

The pool opened in December 2006 after nearly five years of construction work and is said to have set developers back as much as $1.6 billion.

And on top of that eye-watering initial cost, it takes a further $3.2 million a year to keep it in working order.

Crystal Lagoons at the San Alfonso del Mar resort in Chile is the world's largest outdoor pool with more than three fifths of a mile in length

It uses a computer-controlled suction and filtration system to suck water in from the ocean at one end and pump it out at the other, while the sun warms it to 26C – nine degrees higher than the sea.

The pool’s incredible dimensions leave the next biggest floundering in its wake, with the Orthlieb in Morocco measuring a mere 1,575 ft long.

 Crystal Lagoons in numbers:

• Capacity: 66 million gallons

• Length: 3,323 ft

• Area: 20 acres

• Depth: Up to 115 ft

• Temperature: heated to 26C

• Estimated cost of construction: $1.6 billion

• Cost of upkeep: $3.2 million a year

• Construction time: almost 5 years

• Completed: December 2006

• The competition: More than twice the length of the next biggest outdoor pool

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