Fallingwater
Fallingwater is the common name for the Edgar Kaufmann house at Bear Run, Pennsylvania, which was designed by American architect Frank Lloyd Wright in 1935.
Edgar Kaufmann Sr. was a successful Pittsburgh businessman. His son, Edgar Jr., studied architecture under Wright briefly. The Kaufmanns owned some property outside of Pittsburgh with a waterfall and some cabins. When the cabins at their camp had deteriorated to the point that something had to be rebuilt, Edgar Jr. convinced his father to hire Wright.
Initially, the Kaufmanns assumed that Wright would design a house that would overlook the waterfall. Wright asked for a survey of the area around the waterfall, including all of the boulders and trees. Wright positioned the house over the waterfall.
Wright adapted the vocabulary of International Modernism—a usually stark and ordered variety used in public buildings— for this organically designed private residence intended to be a nature retreat. The house is well-known for its connection to the site: it is built on top of an active waterfall which flows beneath the house. The fireplace hearth in the living room is composed of boulders found on the site and upon which the house was built. Wright had initially intended that the boulders would be cut flush with the living room floor, but they were left as they were, protuding from the rest of the floor.
The active stream, immediate environment and the cantilevered design of the house are meant to be in unison, in line with Wright's interest in making buildings that were more "organic" and which thus seemed to be more engaged with their surroundings.
The Kaufmann House is now a museum, and undergoing an ongoing restoration. Like many Wright buildings, it was made of somewhat flimsy (often "experimental") materials and has not held up particularly well.
The house had structural problems from the beginning. The contractor built the forms for the reinforced concrete terraces without taking into account the fact that even cured concrete sags a bit after the forms are taken away. The terraces at Fallingwater sagged several inches in the first few years.
In 1996 the Western Pennsylvania Conservancy began an intensive program to preserve and restore Fallingwater. After much study, they added some more steel; post-tensioning the concrete sixty years later.