A lengthy underwater system consisting of two separate branches converging at the Polldeelin resurgence. There are two entrances at the risings - one accessing each branch - with a passageway between them that has been artificially filled in with debris placed in an intermediate shakehole. This has separated the two branches into two separately accessible caves. Since they were once connected and could be again by removing the debris, they are treated as a single cave system here.
The first branch is the Polldeelin to Polltoophill branch, a 2.4 km dive, dropping to 62 metres depth. With the entrance at 15 metres altitude, the deepest point in the branch is 47 metres below sea level, the fourth deepest known point of any cave in the Republic of Ireland, and fifth in the British Isles.
The second branch is Small Polldeelin or Pollnacapple, which is 1.6 km long, dropping to 71 metres depth, heading towards Pollindre. With the water surface at an altitude of 15 metres, the lowest point in the cave is 56 metres below sea level, the third deepest known point of any cave in the British Isles.
A brief description of the exploration is available online.