The Augusteum showcases European paintings – with a strong focus on Italian and Dutch masters – from the 15th to the 18th century. It opened in 1867 in a custom-designed Italian Renaissance building as Oldenburg's first art gallery to show off Grand Duke Nikolaus Friedrich Peter's collection. There's English signage throughout. The gallery also features changing exhibitions. It's part of the Museum of Art & Cultural History, all three buildings of which can be visited on a combined Landesmuseum ticket.
Don't miss a look at the painted wall friezes (1878) upstairs in the main staircase: they feature a who's who of several dozen great artists and other figures from antiquity onwards.