Wasserburg Sachsenhagen, Water castle in Sachsenhagen, Lower Saxony, Germany

Wasserburg Sachsenhagen is a water fortress near Sachsenhagen in Lower Saxony featuring a square keep surrounded by water-filled moats and defensive walls. The grounds sit about 2.5 meters above the surrounding landscape and include a two-story administrative building with a hipped roof alongside the medieval core.

Duke Albrecht I of Saxony commissioned its construction in 1250 to secure territory and support settlement of the nearby Dülwald region. In the early 1600s, Count Ernst of Holstein-Schaumburg transformed the military fortress into a residential castle.

The name Wasserburg denotes a castle surrounded by water, a type still visible in the moat-fed lowland of the Sachsenhäger Aue. Since 1969 the former Amtshaus has been privately owned and used for housing, while the keep hosts events of the Heimatverein Sachsenhagen-Auhagen. The former castle grounds are now used as allotment gardens.

The site can be viewed from the surrounding grounds but is not open for interior visits as it remains a private residence. Walking around the perimeter via local paths offers the best way to appreciate the moats and its setting in the landscape.

In 2012, when the Schlosswiese over the former outer bailey became a small park, trenching for utility lines let archaeologists from the Schaumburger Landschaft examine both castle mounds. They found the original ground level at their edges about 1.5 m lower than today, with roughly 4 m of soil built up on the main castle.