Sønderborg Castle

Sønderborg Castle is a historic fortress and museum located in the town of Sønderborg on the island of Als in southern Denmark. The complex contains building fabric dating from the 12th century and later Renaissance-era rebuilding, and it now houses regional museum collections.

Exhibited displays focus on local and regional history, including the castle’s military and civic roles; visitors can tour preserved halls, defensive walls and the castle courtyard. The castle’s waterfront position offers direct views across the Sønderborg Strait.

Originally built as a medieval stronghold, the castle underwent major expansions and stylistic changes through the Middle Ages and into the Renaissance, after which it served varied administrative and defensive functions. In modern times the site has been restored and repurposed as part of Museum Sønderjylland, with conservation work to stabilise older masonry and present historical interiors to the public.

The castle stands within Sønderborg town on the eastern side of the island of Als, immediately adjacent to the strait that separates Als from the Jutland mainland. It is a central landmark of the town and easily reached from local harbours and roads.

• Age and construction: Parts of the structure date back to the 12th century, with substantial Renaissance-period rebuilding and later restorations.
• Waterfront position: The castle stands at the waterfront in the town of Sønderborg on the island of Als, making its moat and quayside location a notable viewing point.

What to See #

• Castle museum: Museum Sønderjylland - Sønderborg Castle occupies restored rooms and exhibitions presenting regional history, military history and local culture across several floors.
• Castle grounds and keep: The castle complex includes masonry defensive walls, a central keep and a courtyard area that illustrate medieval and Renaissance construction phases.