Extreme Engineering

In Japan, plans are on the table to build Sky City, the tallest structure on earth. The towering, vertical city will house more than 100,000 people. Sky City would be home to the world's very first homesteaders in the sky.

Rail travel may yet go intercontinental. In prototypes of floating tunnels, 5,000-mph magnetically levitated trains travel between New York, London and Paris. Passengers would dine and sleep while whales and nuclear subs glide around them.

The world's great cities have always struggled to find a balance between the need to attract more and more people and their ability to transport them efficiently.

Already on the drawing boards, The Bridge rejoins North America and Asia.

Tokyo is one of the most crowded cities in the world. To relieve the stress on a city bursting at the seams, engineers look to build a massive Pyramid over the water, with skyscrapers suspended like peapods within its enormous frame.

The Hong Kong international airport is the largest civil engineering project in history and the largest enclosed space in the world. It is also 16 miles out to sea and built on a platform that was constructed by leveling two small islands.

Daily, ships the size of a city block transport goods through the Panama Canal to make the 50-mile shortcut between the Atlantic and Pacific Oceans. Officials have asked a team of European and American engineers to compete for a winning lock design.

This Swiss monster is the longest tunnel in the world.

The Delta Works, a series of massive, computer-controlled sea barriers and dams, straddle each of the major rivers emptying into the delta. The Measlandkering is a gigantic sea surge barrier.

In a series of engineering firsts, two interstate highways are being rebuilt beneath Boston, sending its traffic 120 feet underground! The "Big Dig" will take more than 30 years to build, but not without confronting unprecedented challenges.