#vertical shaft
- Pit cave — An endokarstic geological formation consisting of a cave or natural cavity developed predominantly vertically, in the shape of a deep shaft or a steep funnel, formed by the chemical dissolution of limestone by infiltrating waters or by the collapse of an underground chamber ceiling. Avens directly connect the ground surface to the subterranean hydrological network, being structures of great interest for speleological exploration and the study of karstic landforms.