The Napoleonmuseum in Salenstein is located in Schloss Arenenberg. The castle, built at the beginning of the 16th century, was bought in 1817 by Hortense de Beauharnais, daughter of Empress Joséphine, first wife of Napoleon I, and wife of Napoleon's brother Louis. It was then completely remodelled under the direction of architect Johann Baptist Wehrle.
The castle was donated to the canton of Thurgau in 1906.
A spiral staircase links all levels of the castle.
The neo-Gothic chapel was added in 1832. It is one of the earliest buildings of this style in Switzerland.