Joint Security Area
Can you believe that concrete block is a border between S. Korea and N. Korea? Joint Security Area (JSA - 공동경비구역) is the only demilitarized zone (DMZ) where S. Korea troops and N. Korean troops stand face-to-face.
That blue houses are used for commit conference but open to tourists as well. When tourists visit there, they actually can cross the border (!!!) so S. Korean soldiers lock the door on the north side. In addition, N. Korean troops observe inside from outside....
I have been there when I was an officer cadet and it was a weird experience because I couldn't believe that as well. After almost 3 years, I was on a duty at the front-line as a platoon leader..... ;)