A look at some of the world's longest railway tunnels

German Chancellor Angela Merkel delivers a speech on the opening day of the Gotthard rail tunnel, t at the fairground in Pollegio, Switzerland, Wednesday, June 1, 2016. The construction of the 57 kilometer long tunnel began in 1999, the breakthrough was in 2010. (Pablo Gianinazzi/Keystone,Ti-Press via AP) (The Associated Press)

FILE - In this Oct. 8, 2015 file photo, a test train drives close to the northern gate of the Gotthard Base Tunnel near Erstfeld, Switzerland. Just like Hannibal in ancient times, Swiss engineers have conquered the Alps burrowing the world’s longest railway tunnel to ease trade and congestion in European trade and travel. (Urs Flueeler/Keystone via AP, file) (The Associated Press)

FILE- In this Tuesday, May 31, 2016 file photo, a train passes in front of the northern portal of the Gotthard Base Tunnel on the eve of its inauguration, in Erstfeld, Canton of Uri, Switzerland. Just like Hannibal in ancient times, Swiss engineers have conquered the Alps burrowing the world’s longest railway tunnel to ease trade and congestion in European trade and travel. (Laurent Gillieron/Keystone via AP) (The Associated Press)

Capping a mammoth 17-year, $12 billion project, Switzerland has built the world's longest railway tunnel: The Gotthard Base Tunnel.

Here's a look at it and others among the longest railway tunnels in the world.

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GOTTHARD BASE TUNNEL, Switzerland

The inauguration of the 57-kilometer (35.4-mile) Gotthard Base Tunnel through the Alps and central Switzerland drew the leaders of France, Germany and Italy for the celebration Wednesday. At its maximum point, the tunnel is more than 2.3 kilometers (1.4 miles) underground, deeper than any other rail tunnel. The 17-year project cost $12 billion but is expected to reap benefits across Europe for years, including faster travel between Italy and points north and less reliance on trucks that were polluting the Swiss Alps air.

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SEIKAN TUNNEL, Japan

This tunnel in Japan reigned as the world's longest railway tunnel for nearly 30 years. It travels 53.9 kilometers (33.5 miles) under the Tsugaru Straits, linking the Japanese islands of Honshu and Hokkaido. While the Gotthard goes deepest underground, Seikan hits the lowest elevation for a tunnel — 240 meters (790 feet) below sea level.

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CHANNEL TUNNEL, between Britain and France

More than 13,000 workers took over five years to complete this 50.5-kilometer (31.4-mile) undersea tunnel between Britain and France, which was inaugurated in May 1994. The Channel Tunnel runs as deep as 75 meters (250 feet) below sea level and had been Europe's longest tunnel until the Gotthard Base Tunnel came along.

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LOETSCHBERG BASE TUNNEL, Switzerland

Inaugurated in 2007, the second-longest Swiss tunnel runs for 34.6 kilometers (21 miles) and is part of the same three-tunnel project in Switzerland as the Gotthard Base Tunnel to its east.

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GUADARRAMA TUNNEL, Spain

This 28.4-kilometer (17.7-mile) tunnel in Spain was inaugurated in 2005 after about 32 months of construction. It links Madrid, the capital, with northwestern Spain.

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Rhoda Shafner contributed from New York.