5. Witanhurst – London, England – 90,000 square feet
Designed by the architect George Hubbard, the Witanhurst was built between 1913 and 1920. The actual owner seems to be Andrey Guryev, a Russion billionaire who bought it in 2008 for $64 million. The property is the second biggest house in London after the Buckingham Palace: it boasts many advantages such as a swimming pool with sauna room and gym, a movie theater and massage parlor. Moreover, the big house has been used on several occasions as a filming location by various production companies to shoot films and television programmes.