Fallingwater, Frank Lloyd Wright's masterpiece, watercolor on 140lb paper. Fallingwater, completed in 1939 and designed by Frank Lloyd Wright for the Kaufmann family near Mill Run, Pennsylvania, is one of the most celebrated works of architecture in American history. Built over a natural waterfall on Bear Run, the house embodies Wright's philosophy of "organic architecture" — the idea that a building should exist in harmony with its natural environment rather than imposing upon it. The structure is defined by its dramatic cantilevered terraces of reinforced concrete that seem to float horizontally over the rushing stream below, anchored by walls of local sandstone that rise vertically from the landscape. Large expanses of glass blur the boundary between interior and exterior, while the sound of the waterfall permeates every room. Wright didn't merely place the house beside the waterfall — he made it an integral part of it, creating a breathtaking synthesis of human shelter and living landscape that has earned Fallingwater recognition as a National Historic Landmark and one of the greatest buildings ever constructed.