Denmark! The birthplace of the LDN bike, designed by KiBiSi, which has a unique one-piece shape that's as stylish as it is weird.
Its frame is made from carbon fibre sheets formed and layered to make a stiff and lightweight one-piece monocoque structure. LDN's form is derived from a wishbone, linking all the necessary components of the drive steering and drives systems in the most direct and economical way possible. The hole is there to lighten the bike's mass and to provide a detail from which to hang the bicycle on the wall, thereby saving space in restricted urban interiors.
So despite most of the frame being 1 flat piece, the bike is still hangable. They're built to order, and if you're interested, hit up their website. [Biomega]