The jamb leans slightly inward, as early Irish church doorways typically do, and beside it hangs half a broken lintel, cracked when someone tried to lever it free for building material. The other jamb is gone entirely, its blocks prised out of the wall and carried off. By 1868, one observer called this doorway the finest of its type he had encountered, which makes its deliberate dismantling all the more dispiriting to contemplate. A graveyard lies to the south of the church, and a round tower stands only about three metres to the north, the whole complex once enclosed within a substantial square cashel, or stone enclosure wall, fragments of whose foundations are still traceable at ground level.

The site takes its name from Dysert Aonghasa, meaning the hermitage or desert of Aonghas, and belonged to the Céile Dé movement, a reform-minded monastic tradition whose name translates roughly as Clients of God. The Aonghas in question appears to have been Aonghas of Tallaght, a scholar-monk who composed the Féilire Aonghasa, a metrical martyrology listing saints for each day of the year. According to a late twelfth-century preface attached to that work, his life's journey took him from a church bearing his name at Dysert, through Coolbanagher in Laois, where he is said to have begun the martyrology, and finally to Tallaght, where he completed it. He died sometime between 815 and 830, with his feast day falling on the 11th of March, and was reputedly buried at Clonenagh in Co. Laois. The monastery at Carrigeen is first recorded in the Annals of the Four Masters under the year 1033, which notes the death of Conn, son of Maelpadraig, erenagh, or hereditary lay steward, of both Mungret and Dysert Aonghasa, linking this site administratively to the larger monastic settlement of Mungret some 13 kilometres to the north-northeast. The present church fabric dates mainly from the fifteenth or sixteenth century, though it incorporates earlier masonry, and the head of a late fifteenth-century window was recovered from the site.

The ruins lie in Carrigeen townland and are designated a National Monument. The church is a simple rectangle, internally around 16.45 metres long by 5.5 metres wide, with walls roughly a metre thick. The 1840 Ordnance Survey letters noted walls still standing about 4.26 metres high, built of enormous limestone blocks laid in fairly regular courses. Visitors looking closely at the south wall will notice the contrast between the large, somewhat polygonal rubble masonry of the older eastern section and the more uniform later rebuilding elsewhere. The surviving doorway fragment, with its red sandstone dressings set against the grey limestone of the surrounding wall, rewards a careful look. The round tower immediately to the north is a separate structure and a companion monument in its own right.