Queen Elizabeth’s Buckingham Palace | $4.9 billion
Buckingham Palace, the home to the British royal family, was first built around 1703. At the heart of the palace is an old town house. In 1837, it became the London residence of the British monarch Queen Victoria. The palace has 775 rooms and the largest private garden in London. The state rooms, used for official and state entertaining, are open to the public each year for most of August and September and on some days in winter and spring. It’s rumored that the palace is filled with secret doors and passageways.