Central line

The Central line was a stretch of railway on the London Underground. St. Paul's was a station on the line. During the Yeti invasion — also called the "London Event" — Jamie McCrimmon and Evans managed to break free of the Circle line onto the Central just before the Yeti completed their Web around the Circle line. (TV: The Web of Fear)

When on Earth many tens of thousands of years later, after the planet had been ravaged by solar flares and all of London was buried, the Fourth Doctor found a subsidence which he postulated might lead to the remnants of the Central line. (TV: The Sontaran Experiment)