Episode 22

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.

New York City struggles to balance attracting more people with the ability to transport them efficiently. After decades of neglect, the city's subway nears collapse, and a public works project promises a complete overhaul of this once-great system.

A bridge joining North America and Asia holds the promise of unprecedented economic growth on both continents. Already on the drawing boards, the entire bridge would be encased in concrete to withstand fierce Arctic weather and ice.

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.

To most of the world the Alps are a scenic wonder. To merchants and truckers, they're roadblocks and bottlenecks. The 35-mile-long AlpTransit Tunnel is one way to keep Europe moving. Unfortunately, Alpine tunnels stay dangerous forever.

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. These are two of the engineering wonders of the world.

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.

Build the tallest skyscraper in Northern Europe? Only hope they're up to the challenge. And there's a catch: this twisted nightmare of a structure has to complete a 90-degree turn before reaching its final floor, 600 feet up.

Find out what measures are required of Venetians as experts attempt to keep the world's most beautiful city from going underwater.

In a remote corner of France, traffic between the south of France and Paris and the north have run into huge bottlenecks. Designers and engineers are working to open the region by building a bridge to leap across the 1.3-mile wide gorge.

At the world's largest open pit iron mine, a $10 million custom-built super shovel is commissioned to meet a sudden worldwide surge in the demand for iron. Will miners find success with the fastest, most technologically advanced excavator ever made?

New cargo vessels are changing the industry. Shipbuilders are making them so huge, they require the re-dredging and retrofitting of the world's cargo ports and canals.

The Eastern Highland, a vast plateau 100 miles south of the Arctic Circle, is the site of a bold challenge of extreme engineering. World-class tunnel diggers are carving more than 45 miles of tunnels through solid rock hundreds of feet underground.