You could not stay in Prague without seeing the castle which overlook the whole city.

Prague Castle is a castle complex in Prague, dating from the 9th century. It is the official residence of the President of the Czech Republic. The castle was a seat of power for kings of Bohemia, Holy Roman emperors, and presidents of Czechoslovakia. The Bohemian Crown Jewels are kept within a hidden room inside it.

Prague Castle is the largest ancient castle in the world, occupying an area of almost 70,000 square metres (750,000 square feet), at about 570 metres (1,870 feet) in length and an average of about 130 metres (430 feet) wide.