Pit cave

A pit cave, shaft cave or vertical cave—or often simply called a pit (in the US) or pot (in the UK)—is a type of natural cave which contains one or more significant vertical shafts rather than being predominantly a conventional horizontal cave passage. Pit caves typically form in limestone as a result of long-term erosion by water. They can be open to the surface or found deep within horizontal caves. Among cavers, a pit is generally defined as a vertical drop of any depth that cannot be negotiated safely without the use of ropes or ladders.