One of those extraordinary projects which looks like a visualiser's dream but which nobody thinks will ever be built is actually nearing completion.
It is the Skywalk bridge - a glass-bottomed horseshoe, with no visible means of support, which will jut out over the Grand Canyon, allowing visitors to look down a terrifying 1,200m. Intended as a source of tourist income for the Hualapai Native Americans, the bridge will open on 28 March. For construction shots and a video see www. ajplus.co. uk/astragal