A major river cave consisting mostly of a single passage containing a large portion of the River Shannon. The original entrance passage (Pollahuna) was through glacial debris, and regularly collapsed. More recently, the cave has been connected to Polltullyard, which provides a much safer entrance, and has now become the normal way in.
Polltullyard is in Co. Fermanagh (N Ireland) while the original entrance is is in Co. Cavan (RO Ireland). The largest portion of the cave lies in Co. Cavan, but I have chosen to move the cave into the Co. Fermanagh section, since it is now entered from the Co. Fermanagh side. If a reliable entrance is made on the Co. Cavan side, I will move it back into that section, to reflect the proportion of the cave that lies in that section.