Clonmacnoise is located a short drive from Athlone town and is well worth a visit during your stay. Founded in Co. Offaly on the Shannon River by St. Ciaran in the 540’s A.D., the monastery would prosper in its outstanding location, neighboring a major trade route (the river), and lying on the border of Leinster and Connacht, whose kings helped support the community. Originally built of wood, the stone structures that define the present-day ruins of Clonmacnoise were not added for several centuries; Temple Ciaran (now called the Cathedral) was the first stone structure, built, according to the monastery’s annals, in 909. Later additions were made in subsequent centuries, like the gothic north doorway added in the 1450’s. Though no significant finds have been excavated of the original wooden settlement, early monasteries analogous to Clonmacnoise at the time tended to be a series of small, circular huts made of wattle and daub surrounding a church, and the entire settlement was encircled in a ditch . The site also boasts two round towers (one missing its upper half), three high crosses, and six other churches. Irish monasteries in the early middle ages were amazing examples of scholarship to the entire continent, and Clonmacnoise was no exception. One of the most famous products of its scriptorium was the book of Dun Cow, the earliest known example of literature written in the Irish language.
Additional information can be found on the Heritage Ireland site.