Development began soon after the American release of "Sonic Adventure" in 1999 and lasted 18 months. The game was produced in commemoration of the "Sonic" series' tenth anniversary and was designed to be faster-paced and more action-oriented than the original. The development team also expanded upon the presence of the Chao creatures and other player characters. Its locations were influenced by American locations such as San Francisco and Yosemite National Park. Sega announced "Sonic Adventure 2" in October 1999 and exhibited it at E3 2000. It was released worldwide on June 23, 2001.