In military terms, a demilitarized zone (DMZ) is where military activity is not permited. So it's somewhat ironic that the Korean Demilitarized Zone -- which I visited on my recent Korea vacation -- is one of the places in the world where I've most greatly felt as well as seen the military's frankly quite intimidating presence. (In contrast, contrary to the fears of many pre-1997 Handover, the Chinese military are pretty much close to invisible in Hong Kong post its being handed back to China by the British...!)
Miles before I got to the very center of the Korean DMZ in the form of the Military Demarcation Line (MDL) -- where I got to briefly step on North Korean soil -- in the Joint Security Area (JSA) of Panmunjom, the military presence was already discernible in the form of such as regular sentry posts and miles of barbed wire posted along the sections of the Han River that acts as a natural border between South and North Korea (see the photo at the top of this Photo Hunt entry).
But it was upon getting into the DMZ itself that things really did start feeling rather hairy -- with the situation feeling pretty tense after we were issued a series of injunctions, including "don't point" (because your pointing hand resembles a gun from afar and the North Korean border guards might shoot you as a result) as well as "don't take photos in the area unless you are first given the okay to do so".
Re the two other photos in this entry: the middle photo is of the "Truce Village", with the blue huts containing such as the Military Armistic Commission (MAC) Conference Room -- where talks take place between representatives of the two Koreas -- being under United Nations jurisdiction and the gray hut to the side and large building in the background being North Korea's. And the final photo of this series of three is of a combat-ready South Korean soldier standing in the North Korean side of the actual MAC Conference Room. (The two sides take turns to man it, it seems.)
Incidentally, one of my favorite Korean films is entitled and revolves around the Joint Security Area. Containing moments of wonderful humanity along with painful division, angst and pathos, the 2000 film by Park Chan Wook is one that digs deep to provide audience with revelatory glimpses of the Korean psyche. And yes, I have to say that the film was largely behind my wanting to visit the JSA at some point in my life.