Sennybridge is a village in Powys, Wales. It sits at the point where the Senni river joins the river Usk. The Senni travels a distance of 7 miles (11km) from its source in the Fforest Fawr area of the Brecon Beacons National Park, whilst from Sennybridge, the Usk travels 48.8 miles south east to its estuary at Uskmouth.
The grassy remains of Castell Du (Black Castle) stand on the west bank of the Senni. It's possible that it was begun in 1262 by Llywelyn ap Gruffydd. In 1271 it would have been occupied by his companion Einion Sais.