The Arch at Bryn-y-Bryner, is located near Nannau hall at the boundary of the Llanelltyd community with the Brithdir and Llanfachreth community. The arch is on the Llanelltyd side of an unnamed stream and spans a metalled road leading to Maes Y Bryner Isaf. It is an early 19th century decorative folly-arch built as an estate feature by Sir Robert Williames Vaughan of Nannau in rustic style. It has flanking sections of wall containing arched slits with projecting rubble cills and vernacular projecting voussoirs. The arch was originally capped to give a pedimented effect; 2 large slate-stone lintel pieces formerly performing this function lie nearby.
