With its acknowledged fame in the industrial sector all over the world, Japan holds the honour of having the greatest underwater tunnel. The name of this tunnel is Sekan, which is not only the greatest underwater tunnel but also holds the record for being the largest railroad tunnel in the world. The length of the tunnel measures around 33.4 miles which is equivalent to 53.8 kilometres. It is a marvel to behold the usual passage of trains filled with passengers, that too, underwater. The tunnel's construction was finally accomplished in the year 1988, taking a period of almost about two and a half decades to get built, reflecting the meticulous and painstaking efforts that have gone in the construction of the greatest underwater tunnel of the world. Other underwater tunnels in the world are inclusive of Channel tunnel(which goes from France to England), Tokyo Bay (which is also in Japan), which are also few of the greatest underwater tunnels of the world after Sekan tunnel.
The Eiksundtunell in norway is the deepest and the most top modern subsea tunell in the world
The Seikan tunnel is the longest "underwater" tunnel in total, when you take into account its length both over and underwater, coming in at 2 miles longer than the channel tunnel, however the channel tunnel has the longest section that is actual underwater section of any underwater tunnel in the world, it is also the longest international tunnel in the world and is the longest standard-gauge railway tunnel in the world