Sherlock Holmes and Dr Watson.
While there really is a Baker Street, there was no 221 Baker Street during the years of the Sherlock Holmes stories. Baker Street was very short, less than a mile long. The street ran north to south with numbered addresses ranging from 1 to 85. In 1930 some of the surrounding streets were renamed, buildings were renumbered and Baker Street became much longer. At that point 221 Baker Street was a real address.
Soon after this the building at 221 Baker Street was demolished. A new structure, Abbey House, took its place. Abbey House served as the head office for the Abbey Road Building Society from 1932 until 2002. Today the building is still one of the London offices of Abbey. 8)