Abismo Guy Collet
The Abismo Guy Collet (SP-090) is the deepest cave in South America, and the deepest in the world that is formed in quartzite. Located in a tepui in northern Brazil near the border with Venezuela, this cave was first explored by cavers in 2006 to a depth of 671 meters.
István Cave
The cave is still being explored, but only a part can be visited. Its deepest known area is named "Hell". The most beautiful dripstone structures are the "Mammut's Mouth", "Fairyland", "Column Hall" and "Concert Hall". Due to water filling the cave in 1958 and 1974, the inner caverns are presumably connected with water drains.