St Brendan is chiefly renowned for the semi-legendary Voyage of St Brendan, in which he is said to have set out onto the Atlantic Ocean with sixty pilgrims, searching for the Garden of Eden. If it happened, this would have occurred in around 530, before his travel to the island of Britain. On his trip, Brendan is supposed to have seen a blessed island covered with vegetation; convinced that he had seen Paradise, he returned to Ireland. He also encountered a sea monster, an adventure he shared with his contemporary St Columba. It is not impossible that Brendan may have encountered North America on his journey, in which case Brendan was one of the first European visitors to the New World. Christopher Columbus relied on the legends told of St Brendan as part of his argument that it was indeed possible to travel to Asia by crossing the Atlantic.
Naturally, the story of the seven years voyage was carried about, and soon crowds of pilgrims and students flocked to Ardfert. Thus, in a few years, many religious houses were formed-- at Gallerus, Kilmalchedor, Brandon Hill, and the Blasquet Islands-- in order to meet the wants of those who came for spiritual guidance to St. Brendan.
Later, he travelled in the British Isles and visited Wales and the holy island of Iona; returning to Ireland, he founded a bishopric at Annaghdown, where he spent the rest of his days. He was recognised as a saint by the Irish church, and his feast day is May 16. Having established the bishopric of Ardfert, Brendan proceeded to Thomond, and founded a monastery at Inis-da-druim (now Coney Island), in the present parish of Killadysert, County Clare, about the year 550. He then journeyed to Wales, and thence to Iona, for his is said to have left traces of his apostolic zeal at Kil-brandon ' (near Oban) and Kil-brennan Sound. After a three years' mission in Britain he returned to Ireland, and did more proselytizing in various parts of Leinster, especially at Dysart (Co. Kilkenny), Killiney (Tubberboe), and Brandon Hill. He founded the bishopric of Annaghdown and established churches at Inchiquin, County Galway, and at Inishglora, County Mayo.
His most celebrated foundation was Clonfert, in 557, over which he appointed St. Moinenn as Prior and Head Master. Brendan was interred in Clonfert, and his feast is kept on 16 May.