Alain Robert, known as "Spider-man" for his penchant for illegally scaling the world's tallest skyscrapers, is on his way up the world's tallest: Dubai's dizzying half-mile-tall Burj Khalifa. The 48-year-old Frenchman set off just before 6pm local time, and the trip up was expected to take him six or seven hours, notes the AP. Four hours in, he had scaled two-thirds of the 2,717 feet.
Robert's only concession to organizers is the use of a rope and harness, though he didn't appear to be relying on either. The AP notes that an ambulance waited at the foot of the tower. Robert's previous climbs include the New York Times building, the Empire State Building, Chicago's Willis Tower, Kuala Lumpur's Petronas Towers, and Taiwan's Taipei 101, previously the world's tallest building. Click here for more on Robert. (Read more Alain Robert stories.)