Tourism in Omaha, Nebraska, United States offers visitors history, sports, nature and cultural experiences. Its principal tourist attractions are the Henry Doorly Zoo and the College World Series (CWS). A 2003 study by a Creighton University economist estimated that the CWS added $33.8 million to the city's economy that year. With 1.1 million visitors annually, the Henry Doorly Zoo is Nebraska's most popular tourist attraction. In 2007 Omaha hosted the USA Roller Sports National Championships, along with 10,000 people who auditioned for the American Idol television show at Qwest Center Omaha.