The construction of the Japan to Korea tunnel has long been discussed and appears that progress is being made to make this tunnel a reality:

After almost 30 years of discussions, plans to create an undersea tunnel linking Korea and Japan are beginning to materialize. A research group from both countries agreed on Jan. 8 to form a committee to draw up a specific construction plan. Huh Moon-do, the head of the committee, said the tunnel would not only speed up economic consolidation in Northeast Asia but “also play a key role in pursuing bilateral free trade talks” that are currently stalled.

The route is still being reviewed, but it is almost certain that it will begin in Karatsu, a city in Saga Prefecture of northwestern Japan. As the starting point of the Korean side of the tunnel, Geoje Island is highly likely. Due to technical considerations, the Japanese view the Geoje Island route as the best option. If Karatsu and Geoje are linked, the undersea tunnel will stretch for 209 km (145 km under the ocean), making it the longest in the world.

The biggest obstacle is economic feasibility. Construction costs alone will be 10 trillion yen by the Japanese estimate, while Korea estimates it will have to spend almost W200 trillion (US$1=W1,506). A study by Japan, which is more active about pursuing the project, showed the tunnel would not be economically feasible. The result was the same in a study conducted by Korea.

But the committee as well as members of the research group say it is wrong to gauge economic feasibility based only on construction costs and advantages. Japanese members of the joint research group say the tunnel is very feasible economically if effects including job creation and its ability to revive the construction industry are included.

The group says Korea would see a W13 trillion boost to its construction industry, while Japan would gain W18 trillion. Considering the industrial effects of the project, the group forecast that Korea would see economic benefits worth W54 trillion and Japan W88 trillion.  [Chosun Ilbo]

The project is expensive, but I think Korea would be much better served pouring money into this project instead of building a canal across the country.

I think the tunnel is a great idea though I am concerned about the safety of building a tunnel under the ocean in an area  prone to earthquakes.  If it is feasible and safe to build, I think constructing the tunnel will improve both the economic and political relations between the two countries.  The construction of such a tunnel would also rank as one of the greatest, if not the greatest engineering constructions of all time, which is something both countries could be proud of.