After nearly 20 years of construction, the world's longest rail tunnel opened in Switzerland Wednesday. The 35-mile Gotthard Basel Tunnel is a high-speed rail link under the Swiss Alps that will eventually help slash travel time between Zurich and Milan. Photo: APThe Gotthard Base Tunnel, the longest and deepest tunnel in the world, is due to officially open in Erstfeld at a ceremony on Wednesday, June 1. The tunnel, which has been under construction for the past 17 years, will be 57 km long and will allow trains to travels up to 250kmh, dividing travel time by half between Zurich and Milan, to two and a half hours.