Running deep beneath mountains, rivers, and sometimes bustling cities are the world’s longest tunnels
Quiet marvels of modern engineering, hidden from sight, they are vital to everyday life, carrying drinking water to millions, whisking metro trains between megacities, draining floodwaters, and connect regions once separated by formidable terrain.
Some of them extend way beyond 100 km. Let’s look at 11 of the longer tunnels the world owns.
Photograph: Kind courtesy Daniel Case/Wikimedia Commons
1. Delaware Aqueduct, USA
It supplies New York City’s primary water supply system.
Completed in 1945, it stretches over 137 km, making it one of the longest tunnels in the world.
2. Päijänne Water Tunnel, Finland
It is an important water supply system located in southern Finland, serving the Helsinki metropolitan region.
Completed in 1982, the tunnel runs for approximately 120 km and is drilled entirely through solid bedrock, ensuring durability and protection of the water source.
Photograph: Kind courtesy YuDiao1118/Wikimedia Commons
3. Suzhou Metro Line 3-11, China
At Suzhou, China, is the longest metro tunnel in the world, with a total length of about 86.5 km.
Built between 2019 and 2023, the tunnel connects Suzhou Metro Line 3 and Line 11 at Weiting station.
Photograph: Kind courtesy Robbins
4. Dahuofang Water Tunnel, China
Located in Liaoning province, China, is a major water supply project designed to support the region’s growing demand for drinking water.
Completed in 2009, the tunnel stretches for approximately 85.3 km.
5. Orange-Fish River Tunnel, South Africa
A landmark water supply project of South Africa, the Orange-Fish River Tunnel is the longest continuous enclosed aqueduct in the southern hemisphere. Completed in 1972, the tunnel extends for approximately 82.8 km.
6. Bolmen Water Tunnel, Sweden
An essential water supply infrastructure in southern Sweden under the Bolmen lake, it connects the regions of Kronoberg and Scania.
Completed in 1987, the tunnel spans approximately 82 km.
Photograph: Kind courtesy Alikam1896/Wikimedia Commons
7. Istanbul Metro Line M11, Turkey
This metro line tunnel, that came up in Istanbul, is the longest metro tunnel in Europe, as well as the longest tunnel in Turkey.
Developed between 2023 and 2025, the line extends for approximately 69 km.
Photograph: Kind courtesy PresidenciaMX 2012-2018Alikam1896/Wikimedia Commons
8. Túnel Emisor Oriente, Mexico
A critical wastewater infrastructure project in Mexico City, the Túnel Emisor Oriente was designed to reduce flooding and improve drainage for the metropolitan area.
Completed in 2019, the tunnel measures approximately 62.5 km, making it the longest wastewater tunnel in the world.
Photograph: Kind courtesy Hannes Ortlieb/Wikimedia Commons
9. Gotthard Base Tunnel, Switzerland
A twin-tube railway tunnel running beneath the central Swiss Alps in Switzerland and is recognised as the longest conventional railway tunnel in the world.
Opened in 2016, the two tubes measure 57.1 km and 57.0 km respectively.
Photograph: Kind courtesy W. Bulach/Wikimedia Commons
10.Lærdal Road Tunnel, Norway
Connecting Lærdal and Aurland, in Norway is the world’s longest road tunnel.
Opened in 2000, it stretches for approximately 24.5 km.
Photograph: Kind courtesy WillaMissionary/Wikimedia Commons
11. Yellow Line, India
This line of the Delhi Metro, running between GTB Nagar and Qutub Minar, is recognised as the longest metro tunnel in India. Constructed between 2004 and 2010, the underground stretch extends for approximately 24 km.
