Llys Gwenllian is an earthwork motte and bailey fortress, standing against the steep slope to the Afon Ystrad. The low ditched polygonal motte and the large rectangular bailey platform, are surrounded by a ditch, with the remains of a counterscarp bank. To the north-east, is a possible outer bailey but sadly farm buildings have badly damaged the site, making its layout hard to observe. The castle is associated with a daughter of Llewelyn ap Iorwerth and there is an unlikely suggestion that it's the predecessor or an outpost to Denbigh Castle.