The Power Tower is 65meters high and served as the entrance to the royal way which led through the Old Town, across the Charles Bridge and up to the Castle. Until 1836 this way was used by kings going to the Vitus Cathedral for their coronation.
The Powder Tower was built in 1475, and was one of 13 similar gates that lead into the Old Town. The tower got its current name in the 17th century, when they started to use the tower as gunpowder storage.
Today it is possible to walk up some stairs to the top of the tower. From there you can enjoy a nice view over the Old Town of Prague.
Powder Tower Prague
Powder Tower pictures