Everybody knows about the Chunnel or the Channel Tunnel, an underwater railway tunnel that connects Kent, United Kingdom with Pas-de-Calais, France, via a super-fast "Eurostar" rail transport.

Built in 1974 and Spanning a considerable distance of a little over 50 kilometres, the Chunnel is bone chilling for ones with claustrophobia and anxiety. Murder for ones with an over active imagination and a bathophobia (fear of depth), because its 75 metres or 250 feet under the sea. 

© Cnet

Well, at least 37.9 kilometres of the 50 are under water, which entails an underwater travel time of about 20 minutes at up to a nauseating 300kmph. Ingenious, but freaky. But... did you know there's another underwater tunnel that runs longer and deeper under the sea bed and isn't located in Europe? Any guesses? Hint: It's in the land of Cherry Blossoms...

That's right, Japan is home to the longest and deepest under water rail tunnel in the world called the Seikan. The Seikan Tunnel is about 53.85 kilometres long and 100 metres or 330 feet deep under the sea bed-- that's three kilometres longer and 25 metres or 80 feet deeper than the Chunnel. Does that make you shudder?

© Tofugu

The 91 metre long and 16 metre wide Seikan, that was built in 1988, connects Aomori Prefecture on Honshu Island with the Hokkaido Island using a unique dual gauge rail line system. This system facilitates the movement of the 320kmph super fast Shinkansen Bullet trains in the Seikan, since these special trains require broader gauges than the one used by freight trains passing though the tunnel.

What's disappointing, though, is that even though these trains can go 20kmph faster than the Eurostar, their speed is limited to 160kmph (usual operating speed is 140kmph) in order to avoid potential derailing accidents for low speed freight trains in the vicinity. This is also why most freight trains operate at night time in the Seikan. Knowledge nugget: We might be seeing Shinkansen Bullet trains in India soon as PM Modi has already made a Rs. 8.6 trillion plan to revamp Indian railways by working with the Japanese on this project. Fingers crossed, and back to the under water railways...

© Japan Rail Pass

The only spots where the Chunnel shines brighter than the Seikan is the length of the railway portion that lies under the sea bed and the train operation speeds. The Chunnel extends up to 37.9 kilometres under water as opposed to the 23.3 kilometre long stretch of the Seikan. And, the Shinkansen trains operate at almost half the speed of the Eurostar. 

We aren't complaining, though, it is the longest undersea tunnel in the world... Another thing that might interest you, however, is that the longest underground tunnel in the world is Gotthard Base Tunnel, which is 57.09 kilometre long and about 24.5 kilometres deep below the earth's surface! Still not under water, though, wink wink!

© Swissgateway