黑龙江
The Amur River Tunnel (Russian: , during its construction — стройка No.4) is a 7200-meter-long railroad tunnel on the Trans-Siberian Railroad, in Khabarovsk, Russia. It was built during 1937—42 for giving an alternate route for the Khabarovsk Bridge across the Amur River. This tunnel is the only underwater tunnel in the Russian Railroad System.