The Swiss Alps are an unforgiving landscape of rugged, rocky peaks and lush, green valleys. Connecting communities that would be otherwise isolated by the vast mountain range — including cultural and economic hubs such as Zurich, Milan, and Turin — is no easy task.

Tunneling and track-laying for the 35-mile NEAT Gotthard Base Tunnel has been completed, making it officially the longest tunnel in the world, surpassing Japan's 14-1/2-mile Seikan Tunnel.

Swiss authorities held a media day inside the tunnel on Monday to announce that most of the technical work for the tunnel had been completed, the Swiss newspaper TDG reports. Testing will begin October 1 in anticipation of the first passenger and freight trains in June 2016.