Go Underground

With property values sky-high in posh London boroughs like Chelsea and Kensington, some super-wealthy residents desiring to expand — and who might ordinarily be forced to build up higher — are building down, constructing elaborate, multistory basements instead. In January, CNN reported additions are underway (one covering five floors below ground) for subterranean home theaters, gyms, golf simulators, bowling alleys and even swimming pools.