Known locally as ‘The Bawan’, ‘Doon Fort’ or ‘O’Boyle’s Fort’, this oval cashel measures 36.6 metres northeast to southwest and 25.8 metres northwest to southeast internally. The massive stone fortification dominates the tiny island it sits upon, its walls averaging four metres wide at the base and rising to 4.8 metres in height. Though partially reconstructed, the structure remains remarkably well preserved, offering visitors a tangible connection to Ireland’s fortified past.

The construction techniques employed here mirror those found at the famous Grianán of Aileach, particularly in the distinctive battered style of the walls, which slope inward as they rise. Four sets of steps, each comprising four short flights, allow access to the wall tops where a protective parapet runs along the outer edge. The main entrance, located on the south-southeast side, consists of a 1.8-metre-wide passage through the wall that may have originally been roofed. This entrance reveals the sophistication of the fort’s design; on one side, a ground-level opening leads to a wall passage with steps rising to the top, whilst on the opposite side, an elevated opening accesses a second, narrower passage that eventually turns at right angles to form a low creep entering the cashel’s interior at ground level.

The surrounding landscape of rough, marshy terrain dotted with rock outcrops adds to the site’s defensive advantages and atmospheric setting. Interestingly, this isn’t the only fortification in the lough; the remains of a second, smaller cashel can be found on another island to the west, though only collapsed walling survives. The higher ground level inside the main cashel compared to outside, combined with short stretches of foundation projections at the wall base to the south and north-northwest, suggests careful planning in its original construction, creating both practical defensive features and impressive architectural presence in this remote corner of Donegal.