Prague Castle holds a Guinness record as the largest ancient castle in the world, and the number that explains it is 570 metres — the length of the ridge it occupies, at an average of 128 metres across. Prince Bořivoj put a fortified seat here around 880, and every power since has added to it rather than replaced it: Přemyslid dukes, Holy Roman emperors, Habsburg governors, and Czechoslovak and Czech presidents from 1918 on. The result is not a building but a walled quarter, with three courtyards, two churches, a vineyard, a lane of miniature houses and a Gothic cathedral rising out of the middle of it.
Walking in, the scale takes a while to register: you pass through a gate expecting a keep and find a street. The Old Royal Palace opens into Vladislav Hall, a room whose vault ripples overhead and which once held jousting tournaments indoors. Guards change at the gates on the hour. From the eastern stairs the city drops away below the red roofs of Malá Strana, and after dark the whole ridge is floodlit.