Sometimes called the "Flintstone House" by locals who gape at it as they pass by on I-280, this 1976 William Nicholson design was formed over inflated aeronautical balloons, which was then covered with a frame of half-inch rebar, a coat of sprayed cement.
It's easiest to see from the angle this photo was taken, going north on I-280 and north of Hwy 92.
