Tunneling under the AlpsTo most of the world, the majestic Alps present a scene of wonder. But to European merchants and truckers, they present a troublesome and costly roadblock. Enter the ambitious AlpTransit Tunnel.

At just over 56 miles, this Swiss monster is the longest tunnel in the world. That is, it will be once workers complete this enormous project. Follow a team of miners as they risk death beneath billions of pounds of mountain, slowly but surely carving out massive support and maintenance tunnels. For the main channel, engineers use custom-designed TBMs (Tunnel Boring Machines) – 250 feet long, 33 feet in diameter, with 500-pound drilling heads that pound the rock into submission.

But, it's not as simple as digging a hole. In this subterranean world, rock actually explodes, walls crumble, floods erupt and great rivers of mud are seemingly everywhere. Watch as technicians outfit their men with special laser imaging equipment that helps workers forecast potential fractures and cave-ins. Once a section has been dug, concrete walls are thrown up to keep the newly carved portion from collapsing – but if the concrete dries too fast, it implodes under the pressure, and the mountain comes crashing down. It's just another day at the office for the world's most extreme engineers.

Watch the full documentary now (playlist)