Portions of the following information were taken from technicaldiving.ie

The most intriguing and challenging of all Doolin Green Holes. History of exploration of the longest Irish marine cave (and probably one of the longest marine caves in the world) is paved with great names of cave diving. It was late Ian Rolland who made first serious penetration– after 430m dive in 1987 he reached Pirates Paradise, dry chamber with fine straw gallery. Then Martyn Farr and Brian Judd continued the quest and the same year cave was already 700m long. Soon, 820m from the entrance and off the main route, Merrow’s Mirth – another dry chamber has been found. It was seemingly choked at the end but according to Martyn and Brian it may repay further investigation. Main route continued under the water and in 1991 Martyn reached 900m followed by very low section barely 25cm high. That seemed like a bitter end but in two years time Brian Judd passed the squeeze and extended exploration limits to 935 m meeting junction and another low section.