Boybuloq Cave
The cave is the deepest known cave in Asia having been explored to a depth of from the entrance. At the lowest discovered level a water-filled siphon blocks further exploration. It is thought that the cave has the potential to be the deepest known cave in the world, with a theorised depth of making it deeper than the Veryovkina Cave. The explored length of the cave is .
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.