Tower of London
London, Greater London, England
The core of this most famous (and infamous) of English castles is the stern, square White Tower, begun by William the Conqueror immediately after his conquest. William wanted a "statement" to intimidate the unruly Londoners, and he got it. 90 feet tall, with walls 15 feet thick and a single door reached by a temporary stair made for strong defenses. The original tower was added to and surrounded by a succession of outer defenses over the centuries.