Grafenburg, Island castle and town hall in Lauffen am Neckar, Germany.

The Grafenburg is an island castle and the town hall of Lauffen am Neckar, located on an island in the Neckar River. The structure features a rectangular residential tower with thick stone walls and served as an important administrative center for the region across many centuries.

The Counts of Lauffen built the castle in the early 11th century, possibly in response to a planned monastery foundation in 1003. It was first documented in 1127. After the counts died out in 1216–1219, the castle was pledged to the Margraves of Baden in 1219, then passed to the Counts of Württemberg in 1361. Destroyed in the Thirty Years' War, it was rebuilt, and since 1818 it has housed Lauffen's town administration.

The castle owes its name to the Counts of Lauffen, who built it in the early 11th century; their line died out between 1216 and 1219. Since 2006 a museum in the tower has presented the building's history. The former residential tower, 13 by 10.30 metres in plan, still forms the core of the complex used as the town hall.

The castle island is linked to the east bank of the Neckar by a bridge; the Lauffen Neckar bridge crosses the river further south. The Regiswindiskirche stands on the opposite western bank. The tower museum, open since 2006, is reached through the building that now houses the town administration.

This structure is the only island castle along the entire Neckar River and combines both defensive and administrative functions. The combination of these two roles in one building makes it a rare example of medieval multi-purpose architecture.