Wasserturm, Water tower in Old Town, Lucerne, Switzerland

The Wasserturm is a 35-metre octagonal stone tower standing in the Reuss at the centre of the Kapellbrücke in Lucerne. Its slightly leaning shaft rises to a 15-metre roof truss dated to 1339, and its lowest storey is a windowless dungeon with three-metre-thick walls.

The Wasserturm was built after 1262, before the Kapellbrücke, and first mentioned in 1367; its roof frame dates to 1339. It served as a prison and torture chamber until 1759, then held the state treasury from 1759 to 1798 and the city archive from 1804 to 1919.

The name Wasserturm is misleading: the tower never held water but served as a fortified watchtower and corner pillar of the city walls. Since 1892 a colony of alpine swifts has nested in the 15-metre roof space, cared for by the Ornithological Society of Lucerne since 1959 on the city council's behalf; it is the largest such colony in Central Switzerland. The prominent stork's nest on the spire has stood unused for over a century.

The tower is rarely open to the public, usually only in summer, and can be rented for events; since 1939 it has been leased to the Lucerne Artillery Association. Visitors normally see it from the banks of the Reuss or from the Chapel Bridge, which crosses the river at its base.

The lowest level is a windowless, doorless dungeon with walls three metres thick, entered only through an opening in the floor of the room above. It was probably used as a prison until 1759, when it was abandoned. The room above held the state treasury and archives, and from 1892 a colony of alpine swifts has nested in the 15-metre roof space, the largest in Central Switzerland.