Owey Island is perhaps one of the lesser known of the western Donegal Islands, it is found 500 metres off the northern tip of Cruit Island and is only really inhabited during the summer months. For more Owey Island information and for ferry service contact details have a look at the Owey guidebook.
On Owey there is one of the most unusual natural features in Ireland. Living at the furthest north west tip of the island there is a lake on the clifftops overlooking a huge zawn and the Atlantic Ocean below. This is a standard lake and is easily accessible by a short walk along the inland path running north out of the islands village. The lake provides the villages water supply as it feeds the stream running the length of the island back throught the centre of the village.
Directly below this lake lives another lake, this lower lake is 50 metres underground and is accessed by descending a narrow sink hole hidden at the northern end of the upper lake. Its a bit of a queeze and a crawl down the sink hole and in the last third of the way down it is very, very muddy. This takes you to a deep silt beach at the northern end of the narrow underground lake. The lake is the flooded floor of this impressive 150 metre long and 40 metres high cavern and it is fed by both the lake above and the trickle from the ocean at the collapsed cave enterance to the sea. The descent walls into the cavern are covered in a very nice bioluminescence and this makes the cave walls glow under your torchlight beam.
The underground lake is approx 150 metres long and between 8 and 2 metres wide along its entire length. About half way along the lake there is a constriction and there was a little bit of fresh debris (07/03/17) which had fallen from the cave roof 40 or so metres above, which is slightly worrying as the upper lake is directly above here.
http://www.uniqueascent.ie/the_underground_lake
The underground lake ends in an 8 metre wide pool, which we called The Pool of Tranquility as it is a place of complete darkness with no natural light and a surreal haunting silence.