At its centre, a giant pedimented portico sits in a five-bay recessed section, flanked by long projecting wings that push the whole composition outward in both directions. The roof is high-pitched and slightly sprocketed, meaning the lower edge of each roof slope curves gently outward before meeting the eaves, a detail that softens what might otherwise be an imposing bulk. Around the back, the garden front abandons symmetry entirely, giving the house a rather different character depending on which side you approach from.

The house dates from the early eighteenth century and sits directly beside the ruins of Castlemartyr Castle. It appears on the 1842 Ordnance Survey six-inch map simply as "Castlemartyr Ho", but the building visible today owes its scale largely to the second Earl of Shannon, who greatly enlarged it between 1764 and 1771, with further remodelling following in the late eighteenth and early nineteenth centuries. The demesne was carefully shaped around it: the River Kiltha was widened where it passes through the grounds, a deliberate piece of landscape engineering typical of the period. Tucked into the woods to the northwest is an ice house, a stone-lined underground chamber used to store blocks of ice cut in winter for use through warmer months, a luxury feature that speaks to the household's considerable resources. The ballroom retains notable decorative plasterwork. For much of the twentieth century the house served as a Carmelite college before being converted into a hotel in 2007, a transition that has kept the building in use and largely intact while pairing it, somewhat unexpectedly, with a golf course and spa.