A number of flat concrete pads, which delineated an area 17m east-west by 8m on a level area on the southwest side of the Grwyne Fawr river, just below the reservoir. The area was overgrown with grass and nettles when recorded in September 2007 but a wall line could be seen on the east edge of the structure. It seems likely that this is the remains of a building connected with the construction of the reservoir, along with NPRNs 267136 and 267138. According to Rev DA Tipper in his 1975 book Stones and Steam in the Black Mountains, page 45, there were several buildings near here but this may be the remains of the power house. J.J.Hall, Trysor, 27 September 2007