An intact, stone-built building on the northeast side of the Grwyne Fawr river, just above the reservoir. It was well constructed with quoin stones and a slate roof. An internal chimney was visible on the northwest side , a doorway in the southeast side and a window in the southwest. It was identified by Rev DA Tipper in his 1975 book "Stones and Steam in the Black Mountains" as Underwood's Meter House, built in 1915 for the small reservoir above this point, before the main reservoir was built. It appears to be used as a bothy now. J.J.Hall, Trysor, 5 February 2008