Zacatón

Zacatón (El Zacatón sinkhole) is a thermal water filled sinkhole belonging to the Zacatón system - a group of unusual karst features located in Aldama Municipality in the northeastern state of Tamaulipas, Mexico. It is the deepest known water-filled sinkhole in the world with a total depth of 339 metres (1,112 ft). The 392 metres (1,286 ft) deep Pozzo Merro (Italy) is deeper but is rather a near-vertical cave and not a sinkhole.

• http://en.wikipedia.org/wiki/Zacatón