Buckingham Palace is a must-see when you come to London, especially at 11:30 am to watch the Changing of the Guard. This is the official residence of the Queen, and if you get lucky you might just spot her. The city's iconic tower, Big Ben, should also not to be missed, even if you just observe it from afar. Westminster Abbey, the site of royal weddings and coronations, is also worth a visit, as is Tate Modern, the museum of painting and contemporary art.