Thun Castle dominates the old town from its hill above the Aare, its four square towers visible from most points in the city. Built in 1191, it is one of the best-preserved medieval castles in Switzerland and has served as a museum since the 19th century. The collection covers the history of the Bernese Oberland, with armour, weapons, ceramics, and furnished period rooms.
The climb up to the castle is steep but the views from the towers justify the effort. On a clear day you can see across Lake Thun to the Bernese Alps — Niesen, Stockhorn, and on perfect days the snow-capped summits of the Bernese Oberland. The castle gardens are freely accessible even without a museum ticket.