When Swiss engineers completed drilling the Gotthard Base Tunnel Friday, they were lauded for finishing the world’s longest tunnel – but actually it's only the world's longest rail tunnel. Read on to find out what underground structures take the honors for being the longest.
The Seoul Metropolitan Subway's Line 5 is the longest rapid-transit line in the world right now and one of the longest tunnels, period, measuring 29.6 miles underground. The Seoul Metropolitan Subway is one of the most widely used rapid-transit systems in the world, making about 8 million trips a day between all of its lines.
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