Though lines such as Victoria and Waterloo & City focus more on serving central London, some are set up to connect the farthest reaches of the city, allowing passengers to travel great distances without ever changing tubes. The longest of these journeys is on the Central line, from West Ruislip (zone 6 out west) to Epping (zone 6 east- technically in Essex, not London). This trip covers 34.1 miles and takes approximately 90 minutes. Fortunately a fair whack of the Central line is above ground so it's not too grim a trip.