Though dense overgrowth now makes examination difficult, the castle's remains reveal a rectangular tower measuring 12 metres from corner to corner, with walls averaging 0.8 metres thick. Two circular corner towers survive at the northeast and northwest angles; the northwest tower still features two circular musket loops on its south face, whilst a flat-headed window remains visible in the northeast tower.

The castle's history reflects the tumultuous changes in Irish land ownership from the 16th century onwards. Originally known as Annagh Castle, the fortress passed from the O'Molloy clan when Edward O'Molloy, son of Donal O'Molloy, became a ward of Richard Chichester in 1590. By 1621, the surrounding lands of Killananny and Annaghmore had been granted to Sampson Theobalds, a servant to the Lord Deputy of Ireland, Oliver St John. The property changed hands several times through the 17th century, with Terence Coghlan owning it in 1641, John Dow by 1659, and finally the Atkinson family by century's end, who likely received it as part of the plantation scheme.

When the Ordnance Survey documented the site in 1837, they described it as "an island in the centre of a swamp" with "2 round towers, the only remains of an old castle" on its north end, situated west of the largest of two Muddy Loughs. A 100-metre causeway once connected this island fortress to dry land, providing access across the surrounding marshland until 1852, when the Drainage Commissioners cut through it whilst creating a drainage channel. Today, the castle remains surrounded by wet, marshy terrain, with possible wall footings of a bawn wall visible to the southwest, offering visitors a glimpse into Ireland's complex medieval and early modern history.