It is the eastern entrance that rewards closer attention. Flanked by a small guard chamber on either side and roofed with a heavy stone lintel, the doorway opens into a splayed passage that a 1901 sketch by the antiquary Thomas Westropp recorded as once rising to two storeys. When excavations were carried out in June 1999, the lintel had fallen across the passage and rubble choked the entrance completely. What the dig uncovered was a layered history compressed into a single threshold.

The excavation, licensed as 99E0506, established that the elaborate entrance structure was a 14th or 15th-century addition, built after the original cashel wall had been deliberately lowered to accommodate it. A scallop shell recovered from beneath the new foundations was radiocarbon dated to AD 1308, providing a neat terminus post quem for the work. Despite the Westropp sketch suggesting an upper floor, no corbels or stairways were found to confirm one. As FitzPatrick described it in 2009, the structure is mortared rubble masonry throughout, which distinguishes it sharply from the dry-laid prehistoric fabric of the fort itself. The lintel was reinstated and the entrance consolidated in 2001. The fort is concentric in plan, with two enclosing walls set roughly 30 to 45 metres apart and radial walls running between them at the north-west, west, and south-west. Inside the inner enclosure, which measures just over 51 metres on its longest axis, the ground slopes down from a central high point, and the remains of several structures survive against the inner wall, including a small subrectangular building to the south and what may be relatively recent animal enclosures to the north-west. Outside the eastern entrance, a rock-cut fosse, a defensive ditch, originally stone-faced and later backfilled with rubble, runs for over 18 metres before turning west to meet the cashel wall, adding another layer of defence to the approach. Two narrow openings in this area may be the mouths of souterrains, underground stone-lined passages sometimes associated with storage or refuge.

Cahermore sits on the eastern shoulder of a valley running north-east to south-west near Ballyallaban, with open views towards Ballyvaughan and Galway Bay. Dense scrub growth encroaches on the site, so the outer enclosing wall, which survives only from north around to south, and the collapsed radial walls between the two enclosures are considerably harder to read on the ground than the robust inner circuit. A second cashel lies roughly 33 metres to the south-east, and a further enclosure about 60 metres to the east, suggesting this was once a densely settled corner of the Burren.