Records from 1601 place Bishop O’Boyle in residence here, and local tradition dating to the early 19th century credits a Bishop O’Boyle with its construction. The Civil Survey describes the site as having ‘aband’ (possibly a bawn, or fortified courtyard) and ‘one decayed house’, suggesting the castle was already in decline by the 17th century.

In its heyday, the castle and its courtyard reportedly measured an impressive 150 feet square. The structure once featured a round tower on its eastern end, which, along with two gables, stood approximately 40 feet high within living memory. Time has not been kind to these remains; one gable collapsed in 1793, another in 1844, with the tower falling around the same period. The walls were notably constructed with minimal cement, perhaps contributing to their eventual deterioration. Three cannons once defended the island, though two were lost to the lake’s waters during an 18th century attempt to transport them to the mainland, whilst the third remained near the castle as late as 1847.

Today, only about six metres of the western wall survives, standing 3.5 metres high and two metres thick. Within this fragment, a mural staircase, 1.3 metres wide and 1.5 metres high, rises from south to north. The southern section, which narrows to approximately 92 centimetres above the stairs, preserves traces of a simple rectangular window. Grass now covers the lower courses of several other walls to the west, the last vestiges of what was once a bishop’s stronghold on this now landlocked island.