This is the famous atomic clock in the center of Old Town Prague. I have no clue how it works, but it looks pretty cool.
Funny thing about the Old Town. There’s an Old Town, Staré Město, and a New Town, Nove Město, in Prague. This being Europe, the old and new are both pretty old. Staré Město was built in the 11th century, while Nove Město followed in the 14th century. So basically everything in this city was already a few hundred years old when the first settlements in North America were built.