A rectangular structure constructed of mortared stones with brick quoins and located on the summit of Cefn Du. It measures approximately 6m long by 4m wide with walls standing up to 1.2m high. The structure has an entrance on the west side with a possible brick and stone blast wall. The structure is mostly collapsed. Some of the collapsed brick walls have shooting slots or ventilation ports in them, indicating this structure could most likely be a part of the adjacent radio station, or alternatively a shooting hide or a WWII defensive structure. The site is marked on the current OS mapping. P.J. Schofield, OANorth, 7th June 2007