It is not especially large, measuring roughly 26.6 metres north to south and 22.1 metres east to west, and its mortared stone wall has crumbled in places to little more than a metre in height. What makes it worth pausing over is what it was built to contain, and when.

The enclosure was constructed between 1804 and 1806, during the period of the Anglo-French Wars, as a protective perimeter around a stone-built signal tower. Signal towers of this era were part of a coastal surveillance network established along the Irish seaboard to provide early warning of French naval movements, particularly during the years when a Napoleonic invasion of Ireland remained a genuine strategic concern. The tower at Bunnamohaun was one node in that system, positioned to command a wide view of the Atlantic approaches. The enclosure wall and the tower are considered contemporary, built as a single scheme rather than one added to the other at a later date. Tucked into the south-western quadrant of the enclosure is a limekiln, a small stone-built structure used to burn limestone and produce quicklime, likely for mortar during the original construction work. That a limekiln should survive within the same enclosure as the tower it helped to build gives the site an oddly self-contained quality, as though the evidence of its own making was simply left in place when the work was done.