It does not appear on the Ordnance Survey editions of 1836 or 1876, which is itself a small puzzle, since the structure is solidly built and reasonably intact. From the outside it presents a low, beehive-shaped dome of dry-laid stone; inside, the circular space measures just 1.7 metres across and reaches roughly 2 metres in height, roofed with flat slabs laid without mortar. The entrance, facing northeast, is barely 65 centimetres high and 45 centimetres wide, meaning anyone entering must crouch or crawl.

This is a sweathouse, a type of structure once fairly common across Ulster and parts of Connacht, used much as a sweat lodge or sauna might be used elsewhere. The usual method was to heat the interior with a peat fire, rake out the embers, and then occupy the space to sweat out illness or fatigue, sometimes immersing in cold water immediately afterwards. The Coppanaghbane example follows the standard form closely, but a detail recorded by Richardson in 1939 sets it slightly apart: two flues positioned to the left of the doorway. These ventilation features would have allowed some control over the internal heat, a refinement not always found in simpler examples of the type. Richardson's observation, published in 1939, remains the most specific account of the structure's interior that survives.