The building is not merely a church; attached to its west end is a four-storey residential tower, complete with spiral stairs, vaulted floors, small private apartments, and a garderobe, the medieval equivalent of a toilet, built into the wall of the third-floor room. Battlements run along the top of the outer walls, and the lower courses are battered outward at the base for added strength, giving the whole structure the character of a fortified residence as much as a place of worship. Carved into the sandstone above one of the north-wall windows is a sheela-na-gig, a grotesque female figure of a type found occasionally on Irish Romanesque and medieval buildings, whose precise purpose has never been satisfactorily explained. Beside the main doorway, a mutilated sandstone head of a bishop looks down from above the gothic limestone arch.

The place takes its name from the Irish Tigh Munna, meaning the house of Munna, a saint who died in 635. His origins were disputed even in early sources; he has been claimed by the Ceinéal Conaill of Donegal, the Corkaree of Westmeath, and the Corca Oiche of Limerick, which suggests either that he was genuinely mobile in his ministry or that several communities were keen to own his memory. His feast day falls on the 21st of October. The medieval church and its graveyard appear to overlie the site of the early Christian monastery he founded, layers of occupation that stretch across more than a millennium. The church itself was already standing beside a castle by the time the seventeenth-century Down Survey mapped the Corkaree Barony, and it sits today roughly 150 metres south-east of Taghmon Castle, with a motte and bailey, an earthwork castle form introduced by the Normans consisting of a raised mound beside an enclosed courtyard, visible about 350 metres to the south-east.

Inside the ruin, the high barrel vault of the nave survives intact, and a piscina, a shallow stone basin used for rinsing communion vessels, remains in the east end of the south wall, alongside two smaller aumbries, wall cupboards used for storing liturgical objects. The east window is a large pointed opening that appears to have been altered in the nineteenth century, its original tracery and mullions long gone. The upper storey of the tower is open to the sky, but the corbels that once supported a timber roof are still legible in the stonework.