 A group of British teenagers took their enthusiasm for mass transit to the extreme and set a world record in the process. The 18s visited all 272 stations of London's subway system in record time, 18 hours and 8 minutes. The group calls themselves the Amersham Ambushers, a reference to the London suburb they're all from. They had unsuccessfully tried the so-called London Tube Challenge twice before, but the third time was the charm.