For generations of Irish people this has been a place to retreat to, for prayer, fasting and pilgrimage.
Glendalough in Co Wicklow with its famous round tower was one of the most important Christian monastic settlements in Europe.
Skellig Micheal is a World heritage site, site of an ancient Christian monastery and an important wild bird sanctuary.
Knock is famed as the scene of an apparition of the Virgin Mary, St Joseph and St John the Evangelist and draws large numbers to prayer and pilgrimage.
The coming of Christianity brought not just faith but the important skills of reading and writing, until now unavailable to the Celts.