Designed by Frank Lloyd Wright in Pennsylvania, Fallingwater places a house not so as to look at a landscape but directly on top of one — a waterfall. The building's daring rests on a single property of reinforced concrete: the cantilever.

A cantilever is a slab supported only at one end, the other left in the void; the steel reinforcement within reinforced concrete makes this possible by carrying the tensions that concrete cannot. Wright conceived the house's horizontal terraces as cantilevered concrete slabs reaching out into the void from a central stone core and chimney. These slabs hang over the streambed and the waterfall with no visible support beneath them; the house seems to stand in the air above the water. (The reach of the cantilevers pushed the calculation limits of the day; deflection problems that appeared over the years were later corrected by strengthening.)

Wright ties this gesture to his idea of "organic architecture": the building does not stand against the site but grows from it. The vertical core, built of local stone, takes root in the land; the horizontal concrete terraces read as layers naturally extending from the rocks and the water. Inside, the floor is laid over the boulders in place. Fallingwater thus turns the cantilevered concrete slab from an engineering feat into a principle that redefines the relationship between architecture and nature.