In the 18th century a church was set up in the Castle and at the beginning of the 19th century – a prison, a school and an observation tower for port pilots, which has not survived to the present.
The Chapel of the Castle is the oldest preserved church in Kurzeme. For almost two centuries, the prison was located in the Castle. A. Austriņš (1884-1934), a poet and a participant of the Revolution of 1905, was imprisoned here, and after World War II – poet K. Jēkabsons (1879-1946), who also died here.
At present, the restored Castle houses a museum with a permanent exhibition on the history of the Ventspils Castle and the prison. Following the reconstruction carried out during the last decade, the Ventspils Museum is located in the Castle, its digital exhibition on the history of the Castle, the city and the port is considered the most modern in the Baltics.