Roughly rectangular, measuring about four and a half metres by five, it sits at the higher southern end of a coastal platform within the Doonallia fort, a promontory fort being a defended enclosure that uses the natural advantage of a headland, with a constructed barrier cutting off access from the landward side. What makes this particular structure quietly odd is not its shape or size but its company: two other houses of similar character sit close by, their banks so near that one is actually shared between two of them, yet nothing on the surface can tell you which came first, or whether they were ever occupied at the same time.

The bank that defines the house varies considerably as it traces the perimeter. Along the southern side it is narrow and modest, about a metre wide and only 35 centimetres high, with a low rounded profile. Along the eastern side it swells to two and a half metres wide and rises to 80 centimetres on the interior face. At the south-eastern corner someone, at some unknown point, dug a shallow pit into the bank; it is grassed over now, roughly a metre across and only 15 centimetres deep, its purpose unrecorded. A gap of about a metre midway along the eastern side is the most likely location of the original entrance. The interior is flat, but waterlogged, thick with rushes. No date has been assigned to the structure, and no documentary or excavation evidence has resolved the question of when it was built or by whom.