The Zimmertoren (Zimmer Tower) is a 14th-century fortified keep that was once part of Lier's medieval city walls. What makes it unforgettable is the elaborate Jubilee Clock that the local clockmaker and astronomer Louis Zimmer installed on its facade in 1930. The central clock is surrounded by 12 subsidiary clocks showing the phases of the moon, the tides, the zodiac signs, the day of the week, and local time in cities around the world — 57 dials in total, all driven by a single mechanism.
Behind the tower is the even more extraordinary Astronomical Studio, a separate room that Zimmer built privately to house his most complex astronomical instruments. It contains a wave clock, a terrestrial globe, and clocks showing the motion of planets — the work of decades of careful craftsmanship. Entry to both the tower clock and the studio is included in a single ticket. The combination of medieval architecture and obsessive 20th-century clockwork is unlike anything else in Belgium.