The famous Astronomical Clock on the Old Town Hall.
The oldest part of the Orloj, the mechanical clock and astronomical dial, dates back to 1410, when it was created by horologist Mikuláš of Kadaň and Charles University professor of mathematics and astronomy Jan Šindel. The first recorded mention of the clock was on 9 October 1410.Later, presumably around 1490, the calendar dial was added and the clock facade was decorated with gothic sculptures.
Wikipedia
