The two similar concrete-and-glass dwellings — one for Undurraga and his family, the other for a friend and his family — share a common garden, courtyard, and reflecting pool. “My friend thought as I did, that the two houses need to equal one single gesture capable of a dialogue with the extraordinary landscape,” says the architect. Undurraga designed both houses as two-story bridge pavilions that would each span two large cavities excavated into the stone cliff. These cavities were dug so that patios and living/dining areas could be accommodated within them and still have views out of each of the long sides of the houses. The upper levels, devoted to bedrooms and sitting areas, occupy the glazed void under the post-tensioned, reinforced-concrete beams, 150 feet in length. These beams are supported on three piers in each house: One at the center accommodates the fireplace and staircase; the other two, at either end of each house, rest on stone walls or (in the case of the lower levels) merge with them. The concrete floor slabs separating the two levels hang by steel posts from the beams.