Reddit user Shystone has put together some really impressive mashups of classical paintings and Google Street View snapshots of London. They show how much and how little the city has changed in the last few hundred of years.
The one above shows a 1749 Canaletto painting of Westminster Abbey. The Westminster Palace -- which is the home of the House of Commons and the House of Lords -- is missing, because it was built in 1834.
This is a view of the South end of Trafalgar Square, showing a large building that was demolished in 1874.
Here you can see St. Pauls Cathedral at the other side of the river, but no trace of the Millennium Bridge.
Another great view of Trafalgar Square -- its north-east corner of Trafalgar Square, with the Anglican church of St Martin-in-the-Fields.