No. 10 Downing Street is the British Prime Minister's Mansion. In addition to the Prime Minister's Mansion, various departments of the British Government are gathered around Downing Street. The Prime Minister's Mansion is not open to the outside world. It can only be visited by iron railings on both sides of Downing Street. There are guards guarding and iron railing gates. You can watch the changing ceremony here around 11 noon, and you can't miss it if you just pass by.