Falling Water is possibly Wright's most famous work in architecture, considered an architectural masterpiece, the building is situated above a waterfall with free floating platforms. The style of the structure is a fusion between nature and architecture. Using the surrounding enviroment to add style and emphasis to the architecture
Wright evolved a new concept of interior space in architecture. Rejecting the existing view of rooms as single-function boxes, Wright created overlapping and interpenetrating rooms with shared spaces. He designated use areas with screening devices and subtle changes in ceiling heights and created the idea of defined space as opposed to enclosed space.
Sources: http://www.greatbuildings.com/architects/Frank_Lloyd_Wright.html
http://www.howardmodels.com/frank-lloyd-wright/index.html
http://www.examiner.com/interior-design-in-national/remembering-frank-lloyd-wright-part-ii