World Records
The Longest Tunnels in the World: 57 Kilometres Under the Alps
To send high-speed trains through the heart of the Alps, engineers didn't go over the mountains — they went straight through, boring the Gotthard Base Tunnel 57 kilometres beneath rock up to 2.3 kilometres thick. It's the longest railway tunnel on Earth, and at its deepest the rock above presses down so hard the temperature reaches 46°C. But the single longest tunnel of any kind carries no trains at all — it carries water to a thirsty city.