Pen-yr-allt is siuated on a small knoll, immediately south-east of Ty'n y Coed Cottage and some 130m east of Pen-yr-allt farmstead. Historic (1899 and 1905) mapping shows it to be situated on the edge of woodland. Local tradition associates the site with an early church, possibly a chapel or chantry for the nearby medieval hospital of St Mary the Virgin. The adjacent field is reputed to have formerly been known as 'Cae pen y bryn eglwys' or 'Cae pen bryn yr eglwys'. The scale of the structure and its orientation support this interpretation. Excavation in 1906 recovered a number of glazed pebbles, a piece of medieval pottery and a lump of iron slag.
The site is a scheduled Ancient Monument, and its remains consist of the ruins of a substantial rectangular stone building, orientated east-west. Measurements are given as 34ft 6inch length x 16ft width, with walls 3ft thick. Its entrance is in the north wall. The walls are now tumbled and largely turfed over, but still stand up to 1m high.
Sources include:
Archaeologia Cambrensis VI, 1908,viii, 267
Ordnance survey, 1899, first edition 25inch
Ordnance survey, 1905, second edition 25inch
