With apartments costing more than $11,000 a square-foot, London's One Hyde Park is the most expensive apartment building in the world.

The 86-unit complex, which was completed in March 2009, is now more than three-quarters full.

And while most of its residents don't live there full-time (some don't even pay regular property taxes), its owners comprise a roster of the global super-rich that makes buildings like 740 Park Avenue and 15 Central Park West look like tenements.