It is a sweathouse, an indigenous form of thermal bath once found across Ireland, particularly in Ulster and Connacht, in which heated stones were packed inside, the heat allowed to build, and then a person would enter to sweat out illness or fatigue. This one at Cashel is modest even by the standards of the type: a circular interior just 1.4 metres across and 1.8 metres high, with slightly inclined walls drawing up to a lintelled roof, the whole thing built from dry stone and tucked into the land rather than announced by it.

The structure sits on a terrace above an east-west stream roughly 50 metres to the north, and about 40 metres to the east lies an abandoned farmhouse, the two buildings now sharing a landscape of disuse. The proximity of the stream would have been practical rather than incidental; cold water was an essential part of the sweathouse ritual, used to cool the body once the heat had done its work. What is striking about this particular example is how little official attention it attracted for so long. It appears on the 1914 edition of the Ordnance Survey six-inch map, but not on earlier editions, which may reflect the mapping conventions of the time as much as anything about the structure's actual age. Sweathouses are notoriously difficult to date, since they were built simply and repaired without ceremony, and many continued in use well into the nineteenth century.