Gwern-y-Domen is a Norman earthwork motte and bailey fortress, that originally had wet defences. The truncated motte, encased by a ditch with a counterscarp bank, supports a strong D-shaped rampart. A dismantled railway line, separates the remains of the bailey, from the motte and with the dense cover of vegetation, its best view is in winter. One and a half miles west is Caerphilly Castle and 10 miles east is Newport Castle.