From the Swiss Alps to a Japanese metropolis, tunnels can be wonders of modern construction, refuges in a crisis, and scenes of disaster. These are the ten most extreme tunnels on Earth. First, the world's craziest tunnel is the Moscow's Lefortovo. Start with a strong measure of Russian drivers, add some narrow lanes, mix with low light and pour over black ice, and you have a lethal Russian cocktail. With three crashes every day, it's notorious for horrific spine-chilling accidents. Unlike in Moscow, in New York the underground explosions are deliberate. An ambitious new subway line is under construction beneath the streets of Manhattan. It's taken 2000 tonnes of dynamite to blast out 23 new stations. This is the Second Avenue Subway Tunnel. We visit the team of elite tunnellers known as Sandhogs as they deal with a potential disaster, working just feet away from New York's skyscraper foundations. Next the Cu Chi tunnels of Vietnam. They're hundreds of miles long and were built by the Viet Cong, the fearsome Vietnamese resistance army who defeated the Americans and their allies in the Vietnam War. For the western soldiers who had to fight in these tunnels they were the deadliest on earth. We speak to Sandy MacGregor - a young officer in the Australian Engineer corps, and the very first Allied soldier to enter the tunnels. In Kansas we visit Larry Hall at his extraordinary new real estate project. He has bought up two cold war missile silos and is turning them into five star post-apocalypse living - it even has a pool and a fish farm! Next, we take a trip along the Bund Tunnel in Shanghai. A psychedelic magic carpet ride, six hundred and forty seven metres long. This is the weirdest tunnel in the world. Still in China we head to the village of Guoliang. It's perched high on a cliff and so remote that the 350 inhabitants had nothing but a steep mountain path to the nearest road. Until 1972, when the villagers decided to risk their lives and carve out this one mile-long tunnel with only their bare hands and a few pick axes. One of the original builders shows us around. The Salang Pass Tunnel is a product of Afghanistan's war-torn history. Built in haste by the Soviets in 1964, it's been left in ruins by years of conflict. It's also subject to 250 avalanches every year. But despite the damage and dangers the tunnel remains a strategic route through this mountainous country, and we speak to the man who led a ground-breaking renovation project to make this lifeline safer. The Gotthard Tunnel network in Switzerland is the world's largest. But when things go wrong, these tunnels are your worst nightmare. That accident came in 2001. Two trucks collided, and a deadly fire broke out, a mile from the exit. Dozens of people were trapped and 11 died. We meet one of the rescue workers from 2001. The Gotthard network is now also home to an ambitious new project - the Gotthard Base Tunnel. It is the deepest railway tunnel in the world, dug in a mile and a half beneath the mountain peaks. It's also the longest - thirty-five miles end to end. We meet senior technician Stephan Aerni as he performs an important test drive. The mightiest tunnels on the planet are Tokyo's storm drains. Japan lies under threat of Pacific typhoons and when a storm makes landfall, 120 mile per hour wind and pounding rain batter the country. Tokyo is a sitting duck. But it has an ace up its sleeve. A network of tunnels that swallow the floodwater, store it up and then pump it out slowly. It's a giant drainage system for the world's biggest city. Tokyo's typhoon tunnels may be mighty, but size doesn't always matter. On the US-Mexican border, authorities regularly discover state of the art smuggler's tunnels - used to move illegal drugs over the border and into the USA. Welcome to Mexico's infamous drug tunnels: the world's most criminal. We go on patrol with Supervisory Border Patrol Agent Lance Lenoir and see some extraordinary and truly extreme tunnels.