Number 10 Downing Street, London

Ever since Sir Robert Walpole took up residence here in 1721, this rather ordinary, dark brick townhouse has been the official residence for Britain's prime ministers. Behind the world-famous front entrance, with its black door guarded vigilantly by a good old British "bobby," lies a network of formal rooms, offices, private apartments, kitchens and cellars. While access to the general public is strictly forbidden, several hundred school children, selected by visiting MP's, are permitted to visit each year. Situated on Downing Street, Number 10 Downing Street makes a good visit, considering the residents of this house don't even have their own key.