That proximity feels almost absurd beside the antiquity of the place, where a tower inserted into the middle of a medieval church still rises to a restored parapet, and a carved floral window survives in the south gable of the domestic range, an unusual decorative flourish for a monastic building of any period.

The abbey was founded in 1189 under the patronage of Donal Mór O'Brien, king of Thomond, and dedicated to Saints Peter and Paul. It was known in Latin as 'de Forgio', a name derived from the River Fergus on whose western bank it sits, and it functioned as a significant ecclesiastical centre within the medieval diocese of Killaloe. In 1278 the abbey became the scene of a violent internal conflict between factions of the O'Brien family, a clash significant enough to be marked as 'Battle 1278' on the Ordnance Survey six-inch map. After the dissolution of the monasteries in 1541 the property passed to various O'Brien members, yet the Augustinian Canons appear to have remained in occupation until around 1650. The oldest fabric, in the single-aisled church, dates to the late twelfth century, but most of what survives is fifteenth-century work carried out when the Meic Craith lineage held the abbacy. Around 1461, during the reign of Teige Acomhad O'Brien, the church was repaired, the tower built, the well-preserved east window inserted, and the domestic buildings extended. That east window is a three-light opening with reticulated tracery, meaning its stone bars form a net-like pattern in the upper portion, and it remains one of the more complete windows on the site. The tower itself was not original to the church but was pushed into its centre, its piers projecting from the nave walls, with ogee-headed windows at successive levels giving onto both nave and chancel. Excavation in 2005 found fragments of glazed pottery imported from France and small pieces of lead that may once have held the abbey's window glass in place, suggesting the community maintained connections to continental trade well into the medieval period. A wall running east from the north-east corner of the church, on a slightly different alignment, may correspond to a chapel that appears in a sketch of the abbey made by Thomas Dyneley in 1681.

The ruins sit on open ground with wide views across the surrounding landscape, and the flooding that periodically reaches the site, visible in aerial photographs, serves as a reminder of how closely the abbey was always bound to the rhythms of the Fergus. The floral window at the south-east corner of the east range and the view through the tower arch towards the east window repay close attention once inside the enclosure.