Burg Rethem, Medieval castle in Rethem, Germany

Burg Rethem is a lowland castle begun in the 13th century on the eastern edge of Rethem's old town, about 50 metres west of the Aller. In the 16th century it was expanded with bastions, ramparts and moats. Since 2004 the excavated castle foundations have been covered by the Burghof Rethem, a cultural events centre that incorporates surviving masonry.

Burg Rethem was probably built at the start of the 14th century by the Dukes of Brunswick-Lüneburg as a border castle against the County of Hoya; a castle captain and garrison are recorded in 1311. In 1314 Duke Otto II met the Count of Hoya here to settle a dispute, and in 1371 the castle was mortgaged to the Bishop of Verden. From 1386 the castle and town were pledged to the city of Lüneburg for over 200 years, guarding the Aller crossing used by its salt trade.

The site is now the Kulturforum Burghof, a cultural events centre built in 2004 over the excavated castle foundations. Its name recalls the former castle courtyard, and the complex presents historical building remains alongside modern event spaces.

The castle site lies east of Rethem's old town, about 50 metres west of the Aller; the B 209 crosses the river on a bridge just north of it. Excavations in 2000 and 2001 covered only the footprint of the new building, so much of the grounds remains unexamined. The Burghof now serves as a cultural events centre.

The 2000–2001 digs covered only the footprint of the new building, so most of the 50 × 50 m castle yard has never been archaeologically examined. They exposed 2.4 m wide foundations of rubble boulders from a residential and defensive building. Since 2004 these lie beneath the Burghof Rethem cultural centre.