The Underground Lake With Some Of The Most Mesmerizing Blue Water In All Of South America

When it comes to jaw-dropping natural wonders, South America claims some of the world's best. Whether it's Bolivia's Salar de Uyuni salt flats, the Galápagos Islands, the glaciers of Patagonia, or the highest waterfall in the world, this gargantuan landmass is blessed with a staggering amount of outdoor splendors. These treasures aren't just beautiful, but also extremely varied and spread all throughout the continent. You could spend a lifetime exploring what South America has to offer and never quite see it all.

Brazil, of course, has no shortage of such spots. While primarily known for the Amazon rainforest and sun-kissed coastal havens like this beautiful secluded beach, South America's largest country also has numerous attractions that fly well below most travelers' radar.

One such gem is Blue Lake Grotto (Gruta do Lago Azul). This massive cave is filled with pristine freshwater that turns a gorgeous shade of blue when shafts of sunlight hit its surface from a hole in the ceiling. Fed by a yet-to-be-located underground river, the cave's subterranean lake is thought to be 200 feet deep in spots. Even more interesting are the bones of prehistoric animals that lie scattered at the bottom, making Blue Lake Grotto a paleontological treasure trove.

Situated near the city of Bonito in the state of Mato Grosso do Sul, Blue Lake Grotto first attracted attention in 1924 when a local Terena Indian stumbled across it. This was possibly the first time a human had ever entered the flooded cave, and it has since developed into one of the region's top tourist attractions.  

People are drawn to Blue Lake Grotto not only for its magnificent lake but also the speleothem formations that grace the cave. These stalactites and stalagmites help to imbue the cavern with a mystical, otherworldly energy. They also serve as physical reminders of just how old the site is — a single speleothem can take hundreds of thousands of years to develop.

Tourists aren't the only people interested in Blue Lake Grotto. The cave has also attracted scientists eager to unravel its secrets. In 1992, a Franco-Brazilian expedition went diving in the cave's lake and made an exciting discovery: the remains of giant mammals from the Pleistocene era. Thousands of bones from creatures such as saber-toothed tigers and giant sloths lie scattered along the bottom, a veritable gold mine of prehistoric animal fossils.

While Blue Lake Grotto is one of the top attractions in and around the town of Bonito, over the years, the burg has blossomed into a bustling center for ecotourism and makes a great base for further exploration. With clearwater rivers, waterfalls, caves, sinkholes, and hiking routes, the region has loads to offer, and everything can be booked and arranged in town.

Blue Lake Grotto is not the only place near Bonito with incredible water. The area is also home to slow-flowing rivers — most notably the Prata and Sucuri — where visitors can don snorkeling gear and peacefully float downstream while taking in the living, multichromatic world under the surface. The Mysterious Lagoon (Lagoa Misterioso) is another marvel for snorkelers and divers. This flooded cave is over 720 feet deep and features not just cave-dwelling fish but alien rock formations clearly visible in the unspoiled water.

Fans of wildlife and geology should also head to Buraco das Araras, South America's largest sinkhole. This red sandstone crater features a wide viewing platform where visitors can observe the flocks of vividly feathered macaws that call the place home. While you're in the area, make sure to spend a half day at Estância Mimosa. This reserve on a private ranch allows visitors to hike through the forest along the Mimoso River, while stopping off at the numerous waterfalls to swim in the cool, clean pools. For more subterranean underwater adventures, check out Mexico's breathtaking cenotes on the Yucatán Peninsula.