Each summer London’s Serpentine Gallery has commissioned an architect to imagine a new space. “The architects commissioned so far have taken the idea and run with it, invariably assisted by the structural know-how of Cecil Balmond, co-chairman of Arup. But even by the Serpentine’s standards, this year’s design should be something else. It is the brainchild of Dutch visionary and long-time Londoner Rem Koolhaas.”