LaGuardia Airport is hemmed in by river and roads, so designers must push the limits of a tight site by building as tall as possible. This means a vast 120-foot-long escalator is needed to move passengers between floors. But the install hangs precariously in the balance. Below ground the team battles to prevent devastating floods, while above, they build a world-first; twin 450-foot-long pedestrian bridges that allow aircraft to pass beneath.