The longest tunnel in the world is the Seikan Tunnel located in Japan. The tunnel spans a total of 53.85 km or 33.49 miles long.
The tunnel is so long that is passes through the Tsugaru Straight that connects two Japanese Islands. It was opened in 1988 and it is used for the passage of express trains.
The second largest tunnel in the world is the Channel Tunnel located in the United Kingdom. This tunnel spans a length of 50.5 km which is equivalent to 31.37 miles. This tunnel holds the records for the largest undersea tunnel on the planet. It opened in 1994.