During the Early Middle Ages there was a small fort and church on the top of the Thun castle hill. 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 (Rittersaal). The 14 m tall Knights' Hall was built as the centerpiece of a monument to Zähringen power. However, the family never lived in the castle, preferring Burgdorf Castle.
In 1218 it was inherited by the House of Kyburg, who built the upper levels above the Zähringen castle. A quarrel over who would rule the southern Kyburg lands led, in 1322, to Eberhard II von Kyburg murdering his brother Hartmann II at the castle. 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. The Kyburgs ruled over the region for nearly two centuries until a failed raid by Rudolf II on Solothurn, in 1382, started the Burgdorferkrieg. After several decisive Bernese victories the Kyburgs were forced to concede an unfavorable peace. In 1384 Bern bought Thun and Burgdorf, the most important cities of the Kyburg lands. The castle came under Bernese control and became the seat of their local administration.
The massive roof (1430–36) comes from the Bernese period. Due to the lack of residences in the castle, in 1429, an administrative and residential wing was added to the west of the keep, built in late Gothic style, and known as the 'new castle'. The castle was the seat of the local court and since at least the 17th century there was a prison under the roof of the donjon. In 1886 a new prison was built on the castle grounds. Two years later, in 1888, the museum opened in the castle. For a time the jailer was also the ticket seller and guard for the museum.
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. It is open daily between February and October, and on Sundays only for the rest of the year. The great hall is used for concerts or plays, and can be hired for private events.References:
The Broch of Gurness is an Iron Age broch village. Settlement here began sometime between 500 and 200 BC. At the centre of the settlement is a stone tower or broch, which once probably reached a height of around 10 metres. Its interior is divided into sections by upright slabs. The tower features two skins of drystone walls, with stone-floored galleries in between. These are accessed by steps. Stone ledges suggest that there was once an upper storey with a timber floor. The roof would have been thatched, surrounded by a wall walk linked by stairs to the ground floor. The broch features two hearths and a subterranean stone cistern with steps leading down into it. It is thought to have some religious significance, relating to an Iron Age cult of the underground.
The remains of the central tower are up to 3.6 metres high, and the stone walls are up to 4.1 metres thick.