Großbernsau Castle, Medieval castle ruins in Overath, Germany.

Großbernsau Castle is a medieval ruin in Overath with standing wall sections and scattered stone debris from its former fortifications. The remains sit on elevated ground where foundation traces and rubble from multiple structures are still visible.

Built in the 14th century, the castle was probably inhabited until the 18th century. On the death of Wilhelm von Bernsau in 1532 it passed to his son-in-law Goddert van Wylich, then to the families von Schoeller, von Steinen and von Schaesberg. In 1904 Heinrich Reichsgraf von Schaesberg-Thannheim sold the ruin to Johann Dünn, and since 2009 it has belonged to the town of Overath.

Großbernsau was one of eight knightly seats in Overath, alongside Auelburg, Alt-Bernsau, zur Moelen, Vilkerode, Steynhuys, Brambach and Kombach. After Wilhelm von Bernsau died in 1532 the seat passed to his son-in-law Goddert van Wylich, then to the families von Schoeller, von Steinen and von Schaesberg. The name Neu-Bernsau distinguishes it from the older Alt-Bernsau nearby.

The ruin lies in the Agger floodplain in northern Overath and is owned by the town since 2009. In December 2016 the town agreed with the Heimat- und Bürgerverein Overath to open up the overgrown site to the public in time for a commemorative year in 2018, on condition that no costs fall on the town; a descendant of the old knights made the first large donation. Only a roughly four-metre-high outer wall remains, so expect uneven, overgrown ground.

The moated site measures roughly 30 by 30 metres, not the oval 30 by 45 metres sometimes cited, and is enclosed by a small water ditch. Only a stretch of outer wall about four metres high still stands; the tower collapsed during the Second World War. Großbernsau was one of eight knightly seats in Overath, alongside Auelburg, Alt-Bernsau, zur Moelen, Vilkerode, Steynhuys, Brambach and Kombach.