The biggest house in the world is also one of the seats of the British monarchy, the Windsor Castle. Windsor Castle is located in Berkshire, England. It is the oldest continuingly occupied castle. It has about 45.000 square meters occupied by the castles floor. It was first established in 1070 by William The Conqueror, so that means that it is almost a thousand years old! It was originally a wooden castle, standing on the site that is now occupied by the so called Round Tower. Most of the England Kings and Queens left their mark in continuous development of the castle. During the times of war, the currently reigning monarch would build more walls and try to fortify it more heavily. During the times of peace, king or queen would add to it more apartments and rooms for fun and entertainment. The famous college, Eton College is located just across the river Thames some 600 meters from the Windsor Castle. Source: Biggest house in the world