Grosmont Castle is a ruined castle in Grosmont, Monmouthshire, Wales, very near the border with Herefordshire, England, and overlooking a bend in the River Monnow. It is generally considered to have been largely built by Hubert de Burgh early in the 13th century, on an earlier Norman foundation, but was extended in the 14th century. It is located about north-east of Abergavenny, north-west of Monmouth, and south-west of Hereford. The castle ruins are Grade I listed as of 1 September 1956.