Y Castell, depicted on Ordnance Survey mapping as Pencastell, is located some 190m south-west of Capel Mair (NPRN 401200). Although depicted as Pencastell, in 1931 it was known locally as y Castell- the prefix 'Pen' was said to refer to the hillslope only. It is situated some 200m north-east of the recumbent standing stone, Garreg Lwyd (NPRN 303799).

Y Castell is thought to be a medieval castle motte, and is set on a relatively level shelf on north-west facing hillslopes. It is a steep-sided moated mound, about 36m in diameter & rising 6.1m to a summit area some 24m in diameter, dished up to 1.0m deep. An excavation made in the centre of the summit, 'some years' before 1931, reportedly cut through alternating charcoal & soil layers. One of the upper charcoal layers reportedly contained pot sherds & 'thin bones'. In 1931 the field below Y Castell was known by a Welsh name translated as 'the field of the bow and arrow'.

Sources include:
Jones, F.,1931, 'Llangeler Parish: Notes on Some of its Ancient Monuments' in Transactions of the Carmarthenshire Antiquary Society, Vol XXIII

RCAHMW, 18 september 2012