South end (inlet) of the 1 mile 437 yard long Dol-y-mynach Tunnel (outlet end is nprn 261172), carrying water from Dol-y-mynach Reservoir (nprn 309539) to the Foel Valve Tower (nprn 32527), thereby making available the waters of the Claerwen River to the Scheme (nprn 96459).
B.A.Malaws, 24 November 2003.