Subterranean river

The longest subterranean river in the world is the Sistema Sac Actun cave system in Mexico.

[5][6] Some fish (colloquially known as cavefish) and other troglobite organisms are adapted to life in subterranean rivers and lakes.

Dante Alighieri, in his Inferno, included the Acheron, Phlegethon, and Styx as rivers within his subterranean Hell.

The river Alph, running "Through caverns measureless to man / Down to a sunless sea" is central to the poem Kubla Khan, by Samuel Taylor Coleridge.

The characters in Jules Verne's Journey to the Center of the Earth encounter a subterranean river: "Hans was not mistaken," he said.

A subterranean river in the Cross Cave system of Slovenia . (Scale shown by people in photograph.)
The cave of source of the Buna can be entered by boat and dived through a cave system serving as an effluence of the Zalomka .
The Puerto Princesa cave can be entered by boat.
Devil's Throat Cave subterranean river from above
The Effra is one of the subterranean rivers of London . It empties into the Thames by Vauxhall Bridge , from which this photograph was taken.
In Dante 's Inferno , Charon ferries souls across the subterranean river Acheron .