Formed in elevated limestone rock, the system extends to 3.8 kilometres (2.4 mi) of surveyed passage, on two levels.

[2] While the Geological Survey of Ireland in 1859 acknowledged the presence of "caves worn by water, some of which can be traversed for some distance,"[3] positive efforts at exploration were not made until 1981, when the upper part of the cave was explored to a sump, named the "Green Lake".

[4][5] Between 1981 and 1985, further exploration and surveying brought the total length of the cave to 3.81 km (2.37 mi),[1] with a vertical range of approximately 15 m (49 ft).

[5] The entire cave system runs under Castleisland itself, starting at Glounsharoon and ending on the far side of town at the Killarney Road.

The cave was developed between 1987 and 1989 by building a shaft (which is the only man-made entrance) and putting in pathways, railings, lights and a music system.