It’s easy to see where the small town of Pagosa Springs gets its name. With three developed hot spring resorts and several primitive pools, it’s a popular destination for visitors to soak and relax.

The source of many of these springs is the aptly named Mother Spring. Unlike its subsidiary pools, the Mother Spring is not for bathing. And while the other pools are just a few feet deep at most, the Mother Spring reaches depths uncharted.

It is certain that the Mother Spring is the deepest known hot spring in the world, but it is unknown exactly how deep it goes. When it was measured in 2011 by Guinness World Records, they brought a plumb line that was 1,002 feet (305.4 meters) long. The line never hit the bottom, proving that the spring is at least 1,000 feet deep and possibly much deeper. Swimming in the Mother Spring is both dangerous and prohibited. However, it is the source of many other, safer hot spring pools, including the Springs Resort and Spa, as well as several free “hippy dip” springs along the San Juan River.