Yes, for those interested in local history and architecture. It provides insight into Assen's monastic and governmental past, but it is not open to the public beyond the exterior and gardens.
Old Assen Castle, historically known as the Abbey of Assen, is worth visiting primarily for its historical significance and architectural charm. While it is not a traditional "castle" with public interior access, its exterior and the surrounding park (the Abbey Garden) offer a glimpse into the origins of Assen as a settlement around a 13th-century convent.
The site now functions as the Drents Museum. The historic former abbey building houses administrative offices and some exhibition spaces for the museum, which primarily focuses on archaeology, art, and history of Drenthe. A visit to the Drents Museum is highly recommended for a full experience, as it directly incorporates the historical narrative of the old abbey.