Oldenburg Castle stuns visitors in light yellow; its appearance frequently changed over the centuries. At the beginning of the 17th century, Count Anton Günther had his residential seat built in the Renaissance style. Later, the castle façade was endowed with rococo elements. At the end of the 18th century, the library wing was erected, and the castle interior was remodelled in the Classicist style. Some of the historical state rooms are still almost completely preserved today. Large parts of the façade, however, are unmistakeably from the Baroque period.
Since 1921, part of the Landesmuseum für Kunst und Kulturgeschichte (state museum for art and cultural history) has been housed in the castle.