Buckingham Palace is the London residence and administrative headquarters of Queen Elizabeth II. It was originally constructed as a grand house in the 18th century but has been expanded and transformed into a palace over time. The palace contains over 600 rooms, including a ballroom that seats 160 guests, 78 bathrooms, a cinema, swimming pool, and post office. When the Queen is in residence, the Royal Standard flag flies above the palace while the Union Jack flies when she is away. The palace and its gardens are opened to the public during the summer months.