The Gevangentoren, the "Prison Tower," is a 15th-century brick tower built into the sea dike next to the muZEEum. Originally part of Vlissingen's seaward fortifications, it later served as a holding cell for sailors and condemned pirates — hence the name.
The interior has been minimally restored and the climb (steep, narrow) gives one of the best harbour views in the old town. Entry is included with admission to the muZEEum.