Live like our favorite couple from the Stone Age, the Flintstones, in this 1970s home, which is on the market for $4.2 million. According to Curbed, architect William Nicholson constructed the property as “an experiment in innovative building materials.” Spraying concrete on metal frames molded over balloons, Nicholson created the prehistoric-like house in an area between Hillsborough and San Francisco. While the home was built in 1976, the property was remodeled in 2007, bringing its interior up-to-date. Take a looking inside.