Denmark's Borgcenter (Danmarks Borgcenter) is a modern museum built around and into the ruins of Vordingborg Castle. Its permanent exhibition covers the history of medieval castles in Denmark — their construction, their role in wars and trade, and the lives of the people who lived and worked in them. Vordingborg Castle was one of the most important royal strongholds in Scandinavia during the 12th–14th centuries, and the museum makes good use of the physical ruins as context.
The building itself is thoughtfully designed, with large windows looking directly out onto the excavated castle foundations. There is an ongoing archaeological dig at the site, and in summer months you can sometimes watch excavation work in progress. A café is on the premises. The museum is a good rainy-day option if you are spending any time in Vordingborg, and the combination of the museum and the ruins fills a comfortable half-day.