Rich Turn to Pimping Basements

Basements are no longer the lowly underbelly of the high-end home. With the rise of home-theater technology, and widespread community opposition to mansion expansion, wealthy homeowners are increasingly turning basements into underground playgrounds, Portfolio reports, featuring everything from faux-'50s diners to recording studios to saunas. “Whether you have a $2 million house or a $20 million house, finished basements are important," one broker says.

Underground is also a place to stash toys out of place elsewhere. “Things you can't get away with on a main level you can put into a basement,” says one contractor—with water features, arcade games, and the like coming to mind. And new vocabulary is emerging: “I try not to use the term basement," says one enthusiast. “I call it the concourse level.” (More wealth stories.)