At 130 metres (430 ft) vertical depth, it stands joint sixth with Poulnagree in County Clare in the deepest caves on the island of Ireland.

[2][3] The cave is recorded at 5.4 kilometres (3.4 mi) in length (making it the sixth-longest on the island of Ireland),[4][5] but exploration is ongoing and further passage is expected to be found.

The entrance was made in a shakehole adjacent to the sink point of the Hune (pronounced "honey") stream, and close the border in County Cavan.

The initial route was dug through a highly unstable area of glacial fill, making it extremely treacherous.

By the end of August, the team had progressed past several boulder chokes and explored cave passages some 1.6 kilometres (1 mi) in length.

[9] While discoveries were being made in Shannon Cave in 1980, attention was also being paid to a large doline less than a kilometre away in County Fermanagh.

Pitt) and the Irish Caving Club worked together to dig their way into passage leading to a 30-metre (98 ft) underground shaft, with boulder chokes and crawls at its base.

[10] The Pollahune entrance to Shannon was always dangerous, often dumping rocks on passing cavers[11] and finally in 1995 it collapsed, making the cave inaccessible.

During subsequent years attention was turned to Polltullyard, the downstream end of which lay within 60 metres (200 ft) of upstream JCP Passage, according to the surveys.

In early 2008 a team of British cave divers were invited over to dive the sump, now named "Young, Free and Desperate".

"[1]Methodical exploration of high-level leads in St. Patrick's Extension in 2009 led to the discovery of a tight cross-rift intercepting a section of "Paddy's Parade" at right-angles.

[1] A 12 minute VR documentary starring Pam and Tim Fogg based on a LiDAR point scan[15] of the descent into Poltullyard was premiered at IDFA 2023[16] The experience is based on a series of still scenes rendered using proprietary point cloud technology on Unity and runs on the Quest 2.