Visiting The Anhumas Abyss in the Serra da Bodoquena National Park on the outskirts of Bonito in Mato Grosso do Sul is not just one great thing to do in Brazil, it could possibly count as three great things in one. The limestone substrate of the park area makes for cave systems underground, with many still waiting to be discovered, and one in the process of being explored and opened for public visits right now. With small openings, they are difficult to locate and you would probably be happy not to have been the person that first discovered the Anhumas Abyss, as it is two holes in the floor of the forest, one a few metres across, the other a gap just narrow enough to slip down.
You have to descend into the holes to appreciate the beauty of Anhumas, as the two passages soon open out into a huge cavern, around 110m across at its widest point, with a 72m drop to the cave lake that covers the bottom half of the cavern, with a depth of up to 80m. As with the rivers of Bonito, the cave has crystal clear water, with visibility of up to 40m even in the underground darkness. The water contains calcium carbonate from the limestone, meaning that any impurities in the water are calcified and drop to the bed.
Another object that dropped to the bottom was a giant anteater who must have discovered the opening above while snuffling through the undergrowth of the forest, and fell to its death. The skeleton can still be seen in the depths of the lake, resting on the rock.
There are also underwater cones, some of the largest examples of this natural phenomenon yet found on earth. Water drips from fissures in the cave roof to the lake way below, and the calcium carbonate contained in the drips that forms stalactites when falling on rocks, instead forms huge subterranean, subaquatic cones up to 19m tall in parts of the lake. These can all be seen while inside the cave, especially around midday as the vertical sun shines straight through the larger aperture to illuminate the whole cave and like with a spectacular shaft of light.
The Anhumas Abyss takes some work on your part though to enjoy this subterranean natural wonder. First you have to get down there... then you have to get back up! The drop down from the narrow entrance to the lake surface is done by abseiling down, usually in conjoined pairs, and always with the right safety equipment (Bonito is probably the safest place in Brazil in terms of organisation, safety measures and first aid equipment). After such a narrow opening, the sight of the cave opening out below your dangling feet is Part I of this Great Thing to Do in Brazil. The descent takes around 10-15 minutes for most people, sliding down the rope slowly. Once at the wooden platform on the surface, you can take a boat around the lake to spot the shapes of rocks and stalactites around the edges.
The comes Part II. You can change into your wetsuit, don your snorkel and mask, and enter the cool water. Most people snorkel but PADI qualified divers can also dive in the darkness, swimming around the huge cones and visiting the anteater.
Part III is the pull back up, which may not be considered great by everyone. Proper climbing equipment is used for this, and only those who have completed the training session on the 9m practice tower in Bonito the night before are allowed to descend. The long haul takes around 20-25 minutes for people with a reasonable level of fitness. Help is on hand from the top if strictly necessary.
There is a real sense of achievement and satisfaction on emerging once more into the daylight of the forest. A drop into the Anhumas Abyss is a completely unique experience in Brazil, although this may not always be the case if more caves are found. For now though, Brazil Adventure Tours can recommend the Anhumas Abyss as one of the finest activities in the whole country for those who would like a little adventure in their trip to Brazil.
Activity Information: A reasonable level of fitness is required to complete the descent and ascent of the Anhumas Abyss, although no prior caving, rapelling or climbing experience is strictly necessary. All necessary safety equipment and instruction is provided, including the training sessions on the tower an evening or two before. Wetsuit, snorkels, masks and diving equipment for those who require it are also included. Trained instructors are on hand at all times, both during the training, at the entrance and at the lake surface.