Circle line
From Tardis Wiki, the free Doctor Who reference
The Circle Line was a line on the London Underground. It was the major focus of the Great Intelligence's attack on the Underground. British Army Corporal Blake and Craftsman Stephen Weams monitored a map of the Underground with the Circle Line emphasised to show the Yeti's progress.
When Jamie McCrimmon read a map of the system, he discovered that three consecutive stations on the line were Cannon Street, Monument and Tower Hill. (TV: The Web of Fear)
