Can't make it to the Alps for a high-altitude clamber? No matter. Just head to the Olympic Stadium for a walk on the roof. Yup, the roof; that famously contorted steel and Plexiglas confection is ready for its close-up. Just like in the mountains, you'll be roped and hooked up to a steel cable as you clamber around under the eagle-eyed supervision of an experienced guide showering you with fascinating details about the stadium's architecture and construction.