Tunnels: Digging In is one of a trilogy that also includes “Bridges: Reaching Out” and “Skyscrapers: Going Up" . Go behind the scenes of six great tunnels to meet the people who dig them and witness the engineering genius behind these unsung masterpieces. Travel from Japan to Washington, D.C. and experience the grandeur and depth of some of the world's most amazing tunnels. Documentary that examines the most dangerous branch of engineering -- the building of tunnels. The history of tunnel building is strewn with the bodies of workers who perished from drowning, disease or decompression, and while modern tools have made work a bit safer, nothing can remove all of the danger. In the 1970s and '80s, 33 men died constructing the longest underwater passageway on the planet, the 33.5 mile-long Seikan Tunnel (7.5 miles longer than the Channel Tunnel). The program explains how Japanese engineers and miners accomplished the Seikan's 24-year-long dig, taking viewers on a tour deep inside the Seikan's eerie maze of underwater tubes.