An earthen mound, 7m north northeast-south southwest by 6m and 1m high. At the north northeast end was a steel plate or door in the side of the mound which gave access to a chamber in the mound. The south southeastern end of the mound had a hollow in it and was thought to have collapsed into the internal chamber. The purpose of the mound was unknown but thought to be related to the construction of the Grwyne Fawr reservoir in the early 20th century. The mound was covered in grass when recorded in September 2007. NPRN 267128 was a similar mound, although smaller, on the opposite side of the valley. J.J.Hall, Trysor, 27 September 2007