The Tower of London was erected by William the Conqueror in the late eleventh century.  Originally intended to be a fortress and royal residence, it has since become one of London's most popular tourist attractions.  Rumor has it the Crown Jewels are stored there although I didn't get to see them because that would have cost money for admission.  I am not sure when it was added, but the tennis courts are a nice addition to a medieval fortress such as this.  The Tower Bridge straddles the Thames. Many people mistakenly call this London Bridge (which is a few blocks down the river and quite plain looking).