It is not the sort of structure that announces itself. The building is rectangular, roughly 12 metres long and 4.5 metres wide internally, and built of randomly coursed sandstone with dressed quoins, the carefully cut corner stones that give an otherwise rough-hewn wall its structural definition. What makes it quietly strange is the accumulation of modifications layered over its original form: doorways blocked, windows filled in, brick inserted where stone once was, the whole thing gradually sealed and softened by vegetation.

The chapel's original entrance arrangement involved two opposed doorways at the west end of the nave, both now blocked, their almost flat segmental arches still visible beneath the infill. The current entrance is through a pointed arch at the west end, though even this has been altered, with stone removed from the base and brick inserted in its place, suggesting a later and rather pragmatic intervention. One of the southern jambs incorporates tufa, a porous volcanic or calcareous stone sometimes favoured in medieval construction for its workability. The east window is the most architecturally considered element that survives: a pointed arch with a dressed sandstone hood moulding and roll moulding on the interior face. Draw bar holes, the rectangular slots cut into the jambs to receive a wooden locking bar, are also present, indicating the window or an associated opening was once secured. The blocked flat segmental arched windows at the east end of the north and south walls suggest the building went through at least one significant phase of alteration after its original construction.

The chapel is located within the private demesne of Howth Castle and is not straightforwardly accessible to the public. Those who do reach it should expect a building in an advanced state of neglect, with material apparently dumped inside at some point. The ivy cover, while atmospheric, makes a full reading of the exterior masonry difficult, and the interior is not in a condition to be explored safely or comfortably. The east window is the detail most worth seeking out if access allows, as it retains the most legible evidence of the building's original character.