As Wright got older, he experimented more and more with patterns from nature. In 1956 he designed one of his final buildings, the Guggenheim Museum in New York. When he was young and working with Louis Sullivan, he had used abstract designs of prairie plants as decorations on his buildings. He based the design of the Guggenheim on one shape from nature: the spiral. The floor plan is one single fluid ramp spiraling up six stories and resembling the inside of a seashell. The design of the building is part of Wright's continuing crusade to form a new type of American architecture based on forms and styles other than those found in Europe.