At 110 Stories, the Willis Tower (formerly known as the Sears Tower) is the tallest building in North America. As a major landmark and tourist attraction, the building draws 1.6 million people every year to see the view from the Skydeck. But there is another “side” to the tower: It serves as a workplace for 100 different corporate tenants ranging from United Airlines to law firms to the global insurance broker, Willis Group Holdings, who purchased the naming rights in 2009.