The site is naturally defended by its clifftop position, whilst its landward approach is protected by an impressive rock-cut fosse, essentially a deep defensive ditch carved directly into the bedrock. A causeway spanning this fosse marks the original entrance, leading visitors into an interior space that's surprisingly level, save for a curious horseshoe-shaped mound with its own surrounding ditch positioned just south of the entrance. Traces of a low earthen bank can still be seen running around the inner perimeter, suggesting additional defensive features or perhaps the foundations of internal structures.

The fort's most intriguing feature lies hidden beneath the surface: an elaborate rock-cut souterrain that would have served as both storage and refuge during times of danger. This underground complex can only be accessed through its southern opening, where visitors must descend nearly half a metre before entering a passage that runs north to south for just over four metres. The passage opens into a central chamber measuring 3.7 metres east to west, where the ancient builders incorporated both carved rock and masonry construction. Particularly fascinating is a small wall cupboard built into the northern wall, alongside a stone bench or slab supported on stone pillars in the eastern section.

From this central hub, the souterrain branches into multiple chambers and passages, each demonstrating different construction techniques. The western chamber, accessed through a rock-cut opening, extends nearly four metres in length, whilst the northern passage features a properly constructed doorway with a stone lintel and portal stones. Throughout the complex, flagstone roofing protects the chambers, though several openings to the surface provide ventilation and emergency exits. The blocked eastern chamber, visible from above ground, hints at an even more extensive underground network that once existed here. This sophisticated subterranean architecture, combined with the fort's commanding position above the estuary, reveals how Ireland's early inhabitants masterfully combined natural topography with skilled engineering to create formidable defensive sites.