San Diego's cultural focal point is a 1,200-acre park rising immediately to the north of downtown. Velvet lawns, lush gardens and century-old shade trees harbor a world-renowned zoo, outdoor and indoor performance spaces, and a wealth of diverse museums housed in buildings restored from two great world expositions.The land on which the park sits was originally a sandy expanse covered with cacti and chaparral and infested with rattlesnakes. It was set aside for use as a park in 1868 but languished unused until 1892, when horticulturist Kate Sessions leased 30 acres of it for her nursery business. As her rent, she promised to plant 100 trees per year throughout the park and to donate 300 more trees for planting in other parts of the city. Over the next decade, Sessions also cleared brush, dynamited holes in the hard earth for planting, seeded lawns and flower beds, and laid out nature trails.Soon the city took an active role in shaping the park, and by 1910 the landscape resembled its present-day appearance. In 1915 it was the setting for the 1915 Panama-California International Exposition, and in 1935 it hosted the California Pacific International Exposition; the arcaded sidewalks of El Prado and the Art Deco and Mayan structures around it date from these celebrations. Today Balboa Park endures as an idyllic sylvan retreat and the nation's largest urban cultural park.