The site is flanked by deep chasms in the rock, and whoever built here understood that the landscape itself was doing most of the defensive work. A promontory fort is exactly what it sounds like: a naturally defended spur of land, typically cut off or reinforced on its landward side by a wall or earthwork, with the sea or cliffs providing protection on the remaining sides. At Fawnmore, the irregularity of the terrain, an uneven area roughly 80 metres by 54 metres, made formal planning difficult, and the result is a site that reads as much as geology as it does archaeology.

The defining feature along the south-eastern side is a curving wall, now much collapsed, that was originally about 2.6 metres wide and still stands in places to just over a metre in height. It was built in drystone construction, meaning the stones were laid without mortar, and both the inner and outer revetments, the facing walls that held the rubble core in place, survive intermittently along its length. No entrance is clearly visible, which may be a product of collapse rather than deliberate concealment. Just outside the wall sits something equally intriguing: the remnants of a small circular hut, roughly 2.5 metres in diameter. Whether this structure was contemporary with the fort, or represents a later, perhaps unrelated, use of the same headland, is not known. The site has not been subject to formal archaeological investigation, and the details recorded come from information supplied by M. Casey, as noted in Paul Gosling's 1993 archaeological inventory of west Galway.

Inishbofin is accessible by ferry from Cleggan in County Galway, and the northern coast, where the Fawnmore headland sits, is the wilder and less frequented part of the island. The deep chasms that flank the fort make careful footing essential, and the collapsed state of the wall means the site rewards patience and a slow eye rather than a quick glance from a distance.