It was built in the 12th century, today houses the Thun Castle museum, and is a Swiss heritage site of national significance.

[2] The castle was built between 1180 and 1190 by Duke Berthold V of Zähringen, who constructed the still preserved keep to the level of the Knights' Hall (German: Rittersaal).

To protect his newly acquired land from the Habsburgs Eberhard II then sold them to Bern and was promptly given them back as a fief.

[2][3] The Kyburgs ruled over the region for nearly two centuries until a failed raid by Rudolf II on Solothurn, in 1382, started the Burgdorferkrieg (also Kyburgerkrieg).

[7] The castle museum is housed in the five floors of the tower and includes cultural and historic displays showing the development of the region over some 4,000 years.