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 in October to announce that most of the technical work for the tunnel had been completed, the Swiss newspaper TDG reports. Testing is underway, in anticipation of the first passenger and freight trains in June 2016.