Sunlight lighting up the blue waters in the ancient cavern. The cave itself is deep, 328 feet (100 meters) deep, and the lake inside has a depth of about 295 feet (90 meters). Photo #1 by LNarimatsu

Let’s back up at bit, to show you where you are. This is in Brazil, the state of Bonito, Mato Grosso do Sul. Rainbow over rural Bonito. Photo #2 by Sérgio (Savaman) Savarese

Waterfall in Bonito, Mato Grosso do Sul. Bonito is the heart of eco-tourism in Brazil. During the rainy season, from December to March, the vegetation is extremely green and provides plenty of food for the wildlife; the rivers are high and the waterfalls are abundant. Between May and August, there is much less rain so the waterfalls are somewhat less spectacular. Photo #3 by LNarimatsu

Wikipedia explained, “The Pantanal is an ecological paradise right in the heart of Brazil. It is the largest flooded lowland on the planet and the third largest environmental reserve in the world.” Mato Grosso do Sul is “famous for its natural beauty, and is a major destination for domestic and international tourism. The Pantanal lowlands cover 12 municipalities and presents an enormous variety of flora and fauna, with forests, natural sand banks, savannahs, open pasture, fields and bushes. The city Bonito, in the mountain of Bodoquena, has prehistoric caverns, natural rivers, waterfalls, swimming pools and the Blue Lake cavern. Photo #4 by Alicia Yo

Bonito is famous for it’s caving and river activities. “Snorkling in the Rio da Prata.” According to Wikipedia, “Bonito is in the middle of a region which is being discovered as ‘Caribe do Centro-Oeste’ (Caribbean of the Central-West) due to the unbelievable blue color of its waters. Owing to the enormous quantity of limestone in the ground, the water of these rivers passes through a real natural filter where impurities are deposited at the bottom of the river bed, leaving the rivers to be some of the clearest and most transparent in the world.” Photo #5 by Laurian

Fish swimming in the amazingly clear blue waters of Bonito’s River of Silver (Rio da Prata). Photo #6 by David Morimoto

Gorgeous Blue Lake Grotto area has an amazing history because its existence went unknown until 1924. It is believed that no human had set foot in this cave until its discovery by one of the local Terena Indians. Photo #7 by Ygarapé Tour

Blue Lake State Park is where the adventure begins to reach Gruta do Lago Azul or Blue Lake Cave: “The tour starts with a 10-minute walk to the entrance of the cave, which was discovered by a local Indian in 1924. In its interior, after descending 100 meters, it is possible to see the lake of crystal clear water and depth of approximately 90 meters, which makes it one of world’s biggest flooded caves.” Photo #8 by Jonas Henrique

Descending into Blue Lake Cavern. Photo #9 by Roberto Hungria

The name Mato Grosso do Sul literally means ‘Thick Forest of the South’ in Portuguese, a name inherited from its northern neighbor state of Mato Grosso, of which it was part until the 1970s. It is not uncommon for people to mistakenly refer to Mato Grosso do Sul as simply ‘Mato Grosso’.” Blue Lake Cavern entrance. Photo #10 by O Fuji

In 1992 a Franco-Brazilian expedition of cave divers discovered a numerous mammal fossils inside Blue Lake Cave, including the Saber-tooth Tiger and the giant ground sloth called Megatherium americanum meaning “giant beast” which lived during the Plestocine Era – 6000 to 10,000 years ago. Photo #11 by O Fuji

Adventure underground at Gruta do Lago Azul. Photo #12 by ROBINHO Y PACO

Because the cave entrance is so wide, sunlight pours in to light up the cavern and naturally illuminates the clear vivid cobalt blue water. Here, a shaft of sunlight is focused on a cave formation. Photo #13 by Mariana Ricaud

The Blue Lake Cave waters may look shallow but are incredibly deep. You would have no idea that the lake is nearly 300 feet deep. Photo #14 by Roberto Hungria

The cavern is full of different-sized formations, stalactites and stalagmites. Photo #15 by O Fuji & #16 by O Fuji

Gruta Do Lago Azul, or the Blue Lake Cave, is also called the Blue Lake Grotto. Photo #17 by Renan Ogiwara

Looking up from the Blue Lake cavern. Photo #18 by Roberto Hungria

Blue Lake Cave in Bonito Brazil. Photo #19 by ecotourism in Bonito

Gruta do Lago Azul is a part of one of the largest flooded cavities on the planet. Photo #20 by Valdiney Pepper

Besides Blue Lake Cave, another gorgeous ecotourism cave in Bonito is Abismo Anhumas, known as the ‘hole.’ It is relatively new, since it only opened for exploration in 1999. Photo #21 by Explore Caverns Now

Explore Caverns Now explained that Abismo Anhumas visitors rappel 236 feet (72 meters) down through the hole to a floating deck on a crystal clear lake which is 262 feet (80 meters) deep. People can swim or dive among the huge underwater cave formations, some as tall as 65 feet (20 meters). Photo #22 & #23 by Dani Pizzo via Explore Caverns Now

More well-known, yet still as unusual as it is beautiful is to take an adventure caving to see the amazingly blue water at Blue Lake Cave. Photo #24 by Roberto Hungria

Gorgeous reflection at Blue Lake Grotto in Bonito. Photo #25 by escolamaxima