The source of the Shannon river has been traced to the Shannon Pot, alias Pollahuna or ‘ Shannon cave’, at the west end of Cuilcagh mountain. Here much of the underground water is derived from streams originating in Co. Fermanagh.
Immediately north of Cuilcagh lies the Marble Arch cave system, through which flows the Claddagh river. This cave complex can be visited without getting wet, and has a highly informative vistor centre.