The Aille River extends throughout Mayo and is noted for its underground route. Coming from the Partry Mountains, it disappears into the cave at Aille, re-emerging at Ballyburke.
There have been a few attempts to explore the caves; in 1975, some British potholers descended 112 feet into a hole at Pollflanagan, believing it possible to reach Aille cave. This was unproved.
They reported seeing blind fish which survive in the total darkness of the cave. The rise of the Aille is the deepest in Europe. Martin Farr, in 1978, descended 33 metres and believed he had reached the cave floor, but in 2008 Artur Kozlowski, a Polish diver, was able to descend to 103 metres.