Presa El Gasco – Las Rozas de Madrid, Spain - Atlas Obscura

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Presa El Gasco

This 18th-century project to build the world's tallest gravity dam was never completed.  


This impressive 173 foot (53 meters) tall structure is the most significant and intriguing remnant of an 18th-century plan gone wrong.

Presa El Gasco was designed to be the starting point for a waterway extending well over 400 miles (771 kilometers), and dropping over 2,000 feet to Lisbon. A partial collapse and financial problems put a stop to the project years after it was clear no significant shipping could have been supported with the available water supply.

Today, the area around Presa El Gasco is a natural enclave with beautiful vistas of the Sierra, a forested island among one of Madrid’s most exclusive suburbs.

A comfortable 90-minute hike will take visitors from Torrelodones to the actual site. Along the way and only partially hidden by vegetation, additional hints point to the long-gone days of construction such as small aqueducts to divert creeks, foundations of engineers’ quarters, and mounds of solidified lime. 

Know Before You Go

Once at the site, exert caution. Though the dam wall is seemingly solid and sturdy, it has received no significant maintenance in decades.

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