Abismo Anhumas

Abismo Anhumas begins as nothing more than a narrow, steep-walled crack in the ground among the hills outside Bonito, in Brazil's Mato Grosso do Sul. Below it the shaft opens into a huge chamber, and the only way down is a 72-metre vertical rope descent — roughly the height of a 26-storey building — that ends beside an underground lake of startling clarity. Light falling through the slit at the top reaches the water, and visibility below the surface exceeds 30 metres, so that from a floating platform it is possible to look down into the drowned depths of the cave as if through glass.

What lies under the surface is the real wonder. The lake reaches depths of around 80 metres, and rising from its floor is a field of limestone cones — tall, pointed speleothems that grew in the dark and are now submerged — some of them close to 20 metres high. Seen from above while snorkelling or from below by divers, they form a kind of underwater city of spires. The water, fed by seepage and by aquifers running through the region's limestone, holds a steady temperature of roughly 18–20 °C.

The cave came to light around 1970, after a fire cleared the surrounding forest and exposed the opening. In 1983 the geologist Paulo Boggiani and his team reached it and realised that it went down more than 60 metres; they returned in 1984 to map the abyss along with other underground sites in the area, and the cave was opened to visitors in 1999. It is one of the signature sites of Bonito, a town of some 22,000 people that has built its identity around the clear rivers, springs and caves of its limestone country and calls itself Brazil's ecotourism capital. Another of its flooded caverns, the Gruta do Lago Azul, lies in the same district.

Getting there

Abismo Anhumas lies about 23 km by road from the centre of Bonito, in Mato Grosso do Sul. Bonito Airport (BYO), about 13 km from the town, has scheduled flights from São Paulo and Campinas. Campo Grande International Airport, the state's main gateway, is about 300 km away by land.