This is on the private part of Knockadoon and they keep bulls on the island so be very very careful. Follow the path from the gate along by the water and you should be able to spot this pretty quickly.
It is known in folklore as the old hags chair. Ill update the folklore later.
In folklore this cave was the entrance to Tir Na Og. I know that every time I head to Lough Gur I feel like ive been there hours but when I look at my watch im only there for like an hour.
This cave can be found by following the path past Bolin island to the gate the separates Knockadoon which is on private property. Just before the gate on the left you can spot a few paths follow them up and you should be able to find it. Careful though the stones are very slippy.
Lough Gur is packed full of folklore. Plus check out those fadas!
Taken from Sacred Ireland
"It is said that Lough Gur was formed by the goddess Áine who appears here in different forms as mermaid, young woman and hag. As mermaid she rises from her traditional home beneath the sacred waters of the lake, as maiden she empowers the land's human custodians, and as hag she defends her realm.
There was a stone bridge called Cloghaunainey on the Camoge river north of the lake, said to have been demolished in 1930. A story is told of her meeting by this bridge with the 1st Earl of Desmond, the local landowner. Traditionally, it was required of the tribal chief at his inauguration that he seek acceptance of the goddess of the landscape. This was ritualised in a ceremony in Celtic society called a 'feis' which literally means 'to spend the night'. A 'geasa' is a magical prohibition or taboo. When someone is put under a geasa, the penalty for breaking it is usually death.
The story goes like this: the Earl found Áine by the water combing her hair. He crept up on her and took her cloak which immediately put her in his power. She agreed to bear him a son who was be called Géaroid , but warned him that he must never be surprised by anything the son did. ('Iarla' means 'Earl' but 'iarlais' means 'changeling')
The child was born and given to the Earl and grew up excelling in everything. One evening there was a big gathering at the Earl's castle in Knockainy village. A very accomplished young woman appeared out of nowhere and engaged his son in a contest. She leapt right over the guests and the tables and called him to do the same. He hesitated, but his father, wanting him to be bested by a woman, persuaded him to show what he could do. However, he went even further than his father had expected and astonished everyone by jumping into a bottle and out again. His father was so surprised that he broke the geasa put on him before his son's birth. "Now you have forced me to leave you"said the son. And with that he disappeared into the fairy realm.
It is said that he lies sleeping beneath Knockadoon with his knights waiting for a time when they will ride forth and gain freedom for all Ireland. But for the moment he must content himself with riding across the surface of the lake on a milk white horse with silver shoes. According to legend, he must do this once every seven years till the silver shoes are worn away.
Another legend holds that once every seven years the enchanted lake dries up and then the sacred tree at the bottom of the lake can be seen covered with a green cloth. An old woman of the lake can be seen covered with a green cloth. An old woman (Áine as hag) keeps watch from beneath the cloth. She is knitting, recreating the fabric of life. One time a man came riding by just as the lake had disappeared. He snatched the cloth from the tree and rode away. The woman called out and the waters rose, pulling back the cloth and half the horse with it. So Áine continues to protect her realm helped by the waters of the lake."
This is a lovely circle on Knockadoon, I don't think you are technically allowed on the land by the farm owner but it is sometimes open as part of tours.
Circle K, the largest circle on Knockadoon, is located 100m northwest of Circle J. It has an overall diameter of 31m and is made up of two concentric rings (1.2m apart) of more or less adjoining stones. The tallest stone is 1.2m high, but many are much smaller. The entrance is located in the east, and excavation revealed rock-cut postholes that probably held the jambs of a wooden gate of some sort. The presence of a gate suggests that the rings were only part of the original enclosing structure, for one could easily enter it by stepping over the orthostats. These stones may actually have been the inner and outer linings of a taller earthen bank. In the center of the enclosure was a rectangular building, outlined by rock-cut postholes (Figure 4). These features suggest that Circle K may have been a
domestic ring fort, not a ritual stone circle. The pottery found here dates the site to the late Neolithic/early Bronze Age (O'Kelly 1985).
Taken from http://www.nd.edu/~ikuijt/Ireland/Sites/cnoetzel/overview.htm#carraig