Downtown Tucson is clearly laid out; all sights can be easily explored by walking. The second largest city in Arizona is the ideal starting point for excursions to Saguaro National Park, which is divided into an eastern and a western part. Outside the city you can find Biosphere 2, an experimental facility to create a self-sustaining ecosystem, and the Mission San Xavier, an old Spanish mission church. For many years, Old Tucson Studios were the location for the shooting of famous western films and television series.