Old Town Hall Astronomical Clock from the 15th Century. I can't explain how this actually keeps time given that these clocks are actually counting backwards on a 24 hr cycle and are counting not only the time of day, but also the time of the sunrise and sunset, the lunar stage and the calendar day and month. On the hour, the 4 figures - representing the 4 things that the people of Prague feared (invasion, death, greed, and vanity) and the door panels above the clock open and the 12 apostles rotate through the windows while the bells are ringing. It was a pretty cool site to see - especially when you wonder how they created this over 500 years ago