Zimmertoren, Medieval fortified clock tower in Lier, Belgium.

Zimmertoren is a fortified clock tower in the center of Lier that rises roughly 20 meters above the surrounding buildings. The structure displays thirteen clock faces that indicate different astronomical measurements and time calculations, functioning as much more than a simple timepiece.

The tower was built before 1425 as part of Lier's defensive fortifications and served a protective role for the city for centuries. In 1930, it received its astronomical clock system from Louis Zimmer as a tribute to Belgium's centennial of independence.

The tower is named after clockmaker Louis Zimmer, who donated his Jubilee Clock to Lier; it was inaugurated on 29 June 1930, the year Belgium marked its centenary of independence. The twelve dials around the central face show the equation of time, the zodiac, the tides, the phases and age of the Moon, and the Metonic cycle. Lier residents still call the square by the Binnennete the "kade", from its past as a loading quay.

The tower stands on the Zimmerplein, the square on the Binnennete that locals still call the "kaai" after its old loading quay. The astronomical dials are on the tower's front; the Wonderklok and the mechanical planetarium are shown in the adjoining Zimmermuseum pavilion built in 1960. The tower was closed to the public during the roof and window restoration that ran from 2020 to spring 2021.

The slowest-turning hand of the Wonder Clock, kept in the pavilion beside the tower since 1960, needs 25,800 years for one revolution, matching the precession of Earth's axis. Louis Zimmer built the clock for the 1935 Brussels world exhibition; it later travelled to the United States, and Albert Einstein congratulated him on it.