Twelve steps descend to a sunken forecourt, its sides built up with dry-stone walling, which leads south to a low entrance just wide enough for one person at a time. Inside, the cave itself was artificially enlarged to create a chamber roughly fifteen metres long and up to four and a half metres high, its floor carefully laid with narrow cobbles. Stone benches run along both the east and west walls. A recess cut into the west wall, set nearly two metres above the floor, holds a dry-stone table. Light enters from above through a triangular opening in the roof. At the far end of the chamber, four steps descend further still to a D-shaped well.

The archaeologist Gerhard Bersu excavated the site and completed a draft report in 1948, though it was never published. His conclusion was that the cave functioned as a place of worship rather than for any secular or domestic purpose, and he suggested, cautiously, a date somewhere between the twelfth and fourteenth centuries. Karst landscapes, formed by the slow dissolution of limestone, are common in this part of Connacht, and natural cavities in such terrain were sometimes enlarged or adapted during the medieval period. What makes Nymphsfield unusual is the degree of deliberate interior arrangement: the benches, the elevated table-recess, the paved floor, and the well at the end all point to sustained, intentional use over time. The site is designated a National Monument and is in state ownership.