As other climbers prefer to climb only rocks or boulders, the Frenchman, Alain Robert also takes on urban climbing. Thus, he is nicknamed "the French Spider-Man" or "the Human Spider," famous for free solo climbing of skyscrapers without climbing gears, but with only a pair of climbing shoes and a bag of chalk. To successfully climb buildings, he uses protrusions of building walls and windows. His climbs have made him rub shoulders with authorities while also attracting considerable attention and sponsorship. Among buildings he climbed include the Burj Khalifa, Sydney Opera House, Cheung Kong Center, and Petronas Twin Towers.