The park's overall theme is that of a journey of exploration, where guests depart from a main port to visit themed islands, all emphasizing adventure. Initially, the park had six islands. On June 18, 2010, the seventh island, The Wizarding World of Harry Potter (themed to the popular Harry Potter franchise), officially opened at the park. This is Universal's largest investment since opening. In 2013, Islands of Adventure hosted approximately 8.1 million guests, ranking it seventh among United States parks and eleventh worldwide. The eighth island, Skull Island, opened on July 13, 2016.