The Chunnel

Vehicles approach the entrance of the Channel Tunnel on June 27, 2006, in Folkestone, England.

Scott Barbour/Getty Images

The Chunnel, or the Channel Tunnel, is a trio of 31-mile (50-kilometer) long tunnels underneath the English Channel, connecting the United Kingdom and France. When finished in 1994, the Chunnel's $21 billion cost made it the most expensive construction project in history [source: PBS]. Construction involved 13,000 engineers and workers, 250,000 engineering drawings and, sadly, 10 deaths [source: Construct My Future].

Building the Chunnel took six years, but plans for constructing some sort of underwater tunnel spanning the English Channel dated back to 1802, with many false starts along the way. Several pilot tunnels, some thousands of feet long, were dug in the late 19th century. In the 20th century, it took the British and French governments decades to finalize plans for construction. The project was canceled more than once but finally came together in the late 1980s.

­Besides a few incidents of fires, the Chunnel has been largely successful, providing a popular method of transport for people and freight between the United Kingdom and France. But the project's initial cost was severe, and it continues to exact a heavy financial toll. In early 2009, a new rail link connecting London to the British side of the Chunnel opened. It cost $13.8 billion -- the most expensive individual construction effort in the country's history [source: Woodman].