PM Narendra Modi inaugurated India's first under water metro in Kolkata that runs under Hooghly river. Here are the longest tunnels in the world
The world's longest undersea rail tunnel links Japan's Honshu and Hokkaido island. It runs for 53.85 Kilometers
Channel Tunnel spans 50.49 kilometers linking England's Folkestone and France's Coquelles
Tokyo Bay Aqua-Line runs for 23.7 kilometer connecting Kawasaki and Kisarazu in Japan
Located in Norway, this system consists of two tunnels of 14.3 kilometers beneath the sea
Known as Eysturoy tunnel this spans 11.2 kilometers beneath the North Atlantic Ocean
This connects the Danish islands of Zealand and Funen stretching 8.02 kilometers
Situatued in Norway, the tunnel stretches over 7.68 kilometers between the Norwegian mainland and Hareidlandet island