Most agree that Frank Lloyd Wright is the most famous architect of the modern era, if not all of history. Along with Louis Henri Sullivan, his early mentor, he helped form a uniquely American architecture. Wright favored the Prairie School of architecture, which came out of the Midwest United States and emphasized horizontal lines to blend with the landscape. One famous example of his Prairie style home is the Robie House, completed in 1909. Wright took this idea further, however, and promoted what he called organic architecture. This term refers to using both structure and materials to integrate designs with nature and the surrounding environment. Wright was embroiled in scandal in 1909 after he left his wife and family for his mistress. But his career eventually recovered, and he would go on to design many of his signature masterpieces. In 1935, he designed Fallingwater, a home built over a waterfall in southwestern Pennsylvania. Wright was also responsible for the innovative design of the Guggenheim Museum in New York City, which features a rising spiral walkway rather than individual floors.