Buckingham Palace, London

Buckingham Palace in London, official residence of the British monarch since 1837, spans 828,000 square feet across 775 rooms—including 19 state rooms and 78 bathrooms—exceeding the average private mansion by 30 times. Originally built as Buckingham House in 1703 and remodelled by John Nash, its 42-acre private garden houses a helicopter landing pad and lake. While cheaper than the typical rival like Antilia at $5.2 billion estimated value, its historical significance and 92 offices make it a working palace open for 50,000 annual visitors.