Nine hundred years of British history compressed into a single riverside fortress. The White Tower at its core dates from 1078; the surrounding walls, towers, and moat came later, added by successive kings who used the complex as palace, prison, and treasury.
The Crown Jewels are the main draw and worth the queue: the Imperial State Crown, worn at every State Opening of Parliament, is set with 2,868 diamonds. The Yeoman Warder tours — led by the resident Beefeaters in their Tudor livery — run hourly and cover the stories of famous prisoners including Anne Boleyn, Thomas More, and Guy Fawkes with enjoyable theatricality. The armour collection in the White Tower spans five centuries and includes a suit made for Henry VIII's later, considerably larger self.
Nearest tube: Tower Hill.