The Historisches Museum Saar (Saar History Museum) is a museum in Saarbrücken dedicated to the history of the area. Founded in 1985, the museum is housed in an elongated glass building covered by a barrel vault, but most of the exhibition space is located in the basement of Saarbrücken Castle. In fact, the main reason that led to the founding of the museum was the rediscovery, in 1975, of one of the five former Gestapo cells in the basement of Saarbrücken castle, where the Gestapo had its headquarters since 1935. The cell can be visited and today it is one of the most important memorial sites in the Saarland from an educational and pedagogical point of view.

The permanent exhibition in the basement is dedicated to the history of the Saarland in a national and international context, covering a period ranging from the Middle Ages to about the second half of the 20th century. There are objects of art and design, but also many objects of daily use. In addition, the museum leads to the ruins of the Saarbrücken castle complex from the Middle Ages and the Renaissance, 14 meters below the Schlossplatz. The underground castle, a sight unique in Germany, includes a shooting range, fortifications, a ballroom built in the moat, a prison, a secret passage and 16th-century casemates. Information and testimonies on the gradual development of the castle are exhibited: from medieval castle to Renaissance castle up to today's Baroque castle.