Domen Ddreiniog, known in the medieval period as  Tal-y-bont, lies northeast of the village of Tywyn and southwest of Castell-y-bere on the bank of the Afon Dysynni, near what historically was its lowest crossing point.   

This site has been documented as one of the 22 Welsh llysoedd of Gwynedd, though the mound that is visible today has been linked with other motte and Bailey Castles built by the Norman, Robert of Rhuddlan, in his attempt to conquer all of Gwynedd in the late 11th century. After his death, the Welsh retook the area and held it continually until the final conquest of Gwynedd in 1282

It is known that Llywelyn ap Gruffydd himself addressed a letter from the site in 1275, and King Edward I of England visited in 1295.

The motte that is visible today is steep sided and flat-topped, 34m in diameter & 7.0m high. A defensive ditch runs around the base of the mound except on the east side where the motte overlooks the river. The ditch has been reduced by past cultivation and now appears as a less than one meter deep hollow. No traces of other construction or defensive works remain.