Bischofstein Castle, Medieval castle ruin near Sissach, Switzerland.

Bischofstein Castle is a ruined ridge castle on the Chienberg at 698 m, on the boundary between Sissach and Böckten. Its irregular ring wall follows the rock head and is over 1.5 m thick above the ditch, while the round keep has 2.3 m thick walls and an interior only about 3 m wide. A two-room palas stood southwest of the keep, and the original north-eastern gate ramp is still visible inside the wall.

The castle was built around 1250 by the Lords of Eptingen after acquiring land from the Itkon family. A major earthquake in 1356 caused severe damage that shaped the ruins visible today.

The castle's name was chosen deliberately: the Lords of Eptingen handed the site to the Bishop of Basel as overlord and held it back as a fief, first documented in 1311 with Ulrich von Bischofstein. Finds from the ruins point to a comfortable lifestyle, including glazed stove tiles, lead-set window panes, an almost complete brass pan and a bronze padlock.

The ruins are accessible by marked hiking trails from the village of Sissach and the site is well-connected by local footpaths. Sturdy shoes are recommended since the climb to the mountain can be steep and uneven.

The castle was built partly from stone taken from the neighbouring Itkon ruin, which was already crumbling around 1250. The Lords of Eptingen also handed Bischofstein to the Bishop of Basel and held it back as a fief, which is why the fortress carries the bishop's name.