It's a gothic building designed by Matěj Rejsek made in Gothic style. It was built in 1475 as 1 of 13 Prague gates. It's 65 height and it has an exibition: "The life in medieval Prague" inside. As the city grew beyond its old wall, this tower became less important. Now its just a piece of historic work. There is a street starting here, heading towards Prague castle. This is one of the building that is absolutely worth seeing, because it is just few steps from Wenceslav's square.
Picture is taken in front of the building of Czech national bank.