The two ‘must see’ places I had for the south korea trip was the DMZ and Jeju Island. There are several ways of visiting the DMZ but we took the cheapest one which was via the DMZ train seen below. The train allows you to visit the closest point to North Korea. Here you can see through to the other side over the 38th parallel as well as walk through the 3rd infiltration tunnel discovered by the south Koreans. You aren’t exactly on the border but it’s a pretty good way to see North Korea if you weren’t able to arrange a tour with the USO (the only way you can get to the actual border).