South Korea is a mountainous and crowded country. High hills and low mountains are in view no matter where you go, but there are also fifty million people on the peninsula. So, wherever there is flat land, there is a city. The cities, towns, and farms spread over the low-lying areas like water, and nearly all the undeveloped areas are in the heart of mountains.
The DMZ is an exception. Whether it crosses mountains or lowlands, it is wilderness: it stretches blank and empty like a thin belt across the waist of Korea, uncaring of topography. You can track it on a satellite map by the narrow band of darker green marking it out from the towns and farmlands to the southern side. It very roughly traces the 38th parallel of north latitude, extending two kilometers to either side. It is heavily fenced, mined, and guarded, but attracts some visitors, of whom I was one this summer.