1. Seikan Tunnel -- 53.9 km -Japan's Seikan Tunnel is the longest underwater tunnel in the world, and is located beneath the Tsugaru Strait. The tunnel connects Hokkaido Island with the Aomori Prefecture. The tunnel was constructed as the government's response to the unfortunate sinking of five ferry ships due to a typhoon back in 1954, which resulted in public outrage. As engineers saw that extreme weather conditions made bridges too risky, an undersea tunnel would be the safest way to go. The tunnel was completed in March of 1998, which saw the start of all railway transport using the tunnel.
2. Channel Tunnel -- 37.9 km-The Channel Tunnel Connects Folkestone in the United Kingdom to Pas-De-Calais, in northern France. It is owned by Eurotunnel, and has single direction tunnels where the national freight trains, Eurostar, and the Eurotunnel shuttle runs. A central service tunnel is connected to all of the lanes, which also provides access to maintenance and emergency teams. The service tunnel also provides a safety point in the event of an emergency, and passengers would need to be evicted. Special multi-functional vehicles were created for traveling within the service tunnel, designed to arrive at the scene or bring passengers to safety in record time.
3. Tokyo Bay Aqua line -- 15 km-The Tokyo Bay Aqua line is also recognized as a toll highway which spans the Tokyo Bay of Japan. The Tokyo Bay Aqua line opened to the public in December 1997, since planning and construction took 31 years. The tunnel connects Kisazaru City to Kawasaki City; and before the tunnel to cross both cities it required one to drive 100 kilometers along the Tokyo Bay; or to take a ferry.
4. Bomlafjord Tunnel -- 7.8 km-The Bomlafjord Tunnel is part of the Triangle Link Project, together with 3 other bridges designed to connect the islands of Stord, Bomlo, and Fittjar in Norway. The tunnel also forms three lanes of the European Road E39. Construction of the Bomlafjord Tunnel began in 1997, although plans had already been materialized since the 1980's. By 2011, the tunnel began receiving as much as 3,966 vehicles a day. Safety measures have also been integrated into the tunnel;
5. Eiksund Tunnel -- 7.7 km-The Eiksund Tunnel in Norway connects the mainland to Hareidlandet Island, and Eika island. Although it was intended to open to the public in July 2007, construction suffered numerous delays which caused it to open instead on February 2008. It was constructed and is operated by the Norwegian Public Roads Administration, and the same body is responsible for the tunnel's maintenance. The tunnel is divided into three lanes of traffic per day, with 1,000 vehicles crossing it, half of which are freight trucks.
6. North Cape Tunnel -- 6.8 km -The North Cape Tunnel is one of the longest underwater tunnels in Norway, and is located in the Nordkapp Municipality in the northern area of the country. It is located beneath the Magerøysundet strait, and connects Mageroya island to the mainland. It first opened to the public in June of 1999, but before that, a ferry had to carry passengers and freight across the seas from Honningsvag and Kajford. The North Cape tunnel is also a part of the European route E69.
7. Severn Tunnel -- 3.62 km-Located in the United Kingdom, the Severn Tunnel connects South Gloucestershire to Monmouthshire, beneath the River Severn. Construction of the Severn Tunnel was carried out from 1873 to 1886, by the Great Western Railway. Although the tunnel's construction was completed in 1885, it took 14 years before the tunnel could service goods trains and passenger traffic because pumping systems were still unfinished. Before the high speed 1 tunnels were built in London, the Severn Tunnel served as the country's longest mainline tunnel. 8. Vardo Tunnel -- 2.9 km-
9. Sydney Harbour Tunnel -- 2.8 km-The Sydney Harbour Tunnel became operational in August of 1992, and connects the Warringah Freeway to the Eastern Distributor as a means of decongesting the Sydney Harbour Bridge. It is operated by the Sydney Harbour Tunnel Company, but on August of 2022 it will be under public ownership. The tunnel is a twin-tube road tunnel, with two lanes in each direction. Three sections make up the tunnel: the 960 meter immersed tube structure
10. Thames Tunnel -- 0.4 km-The Thames Tunnel is the oldest underwater tunnel in the world and opened back in 1843. People came from across the globe to witness the Thames Tunnel, because it was the first tunnel to be built under a navigable river through the use of tunneling shield technology, which was new at the time. Located under the Thames River in London, United Kingdom; the Thames Tunnel connects the cities of Wapping and Rotherhithe. Although it was originally built for the purpose of horse-drawn carriages,