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.
Sierra de Tamaulipas
In the southeastern part of the Sierra in the municipality of Aldama, Tamaulipas is a limestone karst area in which many caves and cenotes (water-filled sinkholes) are found, including Zacatón which is the deepest sinkhole in the world with a depth of . In 1994, cave-diving pioneer Sheck Exley died attempting to dive to the bottom of Zacatón.