Wealthy home builders around the globe are digging deep.

In Los Angeles, builder Mauricio Oberfeld has buried about a third of his home underground: He built a contemporary 9,000-square-foot house for his family with a 3,000-square-foot basement. Glass stairwells lead to a lower level with an ornately tiled spa, large office, wine room and movie theater.

"What you see from the street looks pretty low-key," Mr. Oberfeld says of the home, completed in 2010. "I don't like to be ostentatious and showing the world."

"Everyone's digging these days," she says.