It is believed the tunnels were built to allow a North Korean military invasion. Each tunnel is big enough, so an entire infantry division can pass in one hour, but the tunnels are too small for tanks or other vehicles. All the tunnels run in a north-south direction and do not have branches. Engineering within the tunnels, following each discovery, has become progressively more advanced. For example, the third tunnel sloped slightly upwards as it progressed southward, to prevent water stagnation. Today, visitors may visit the second, third and fourth tunnels through guided tours.
The first of the tunnels was discovered by a South Korean Army patrol, noticing steam rising from the ground. The initial discovery was met with machine gun fire from North Korean soldiers. Five days later, during a subsequent exploration of this tunnel, U.S. Navy Commander Robert M. Ballinger and ROK Marine Corps Major Kim Hah Chul were killed in the tunnel by a North Korean explosive device. The blast also wounded five Americans and one South Korean from the United Nations Command.
The tunnel, which was about high by wide, extended more than beyond the Military Demarcation Line (MDL) into South Korea. The tunnel was reinforced with concrete slabs and had electric power and lighting. There were weapons storage and sleeping areas. A narrow gauge railway with carts had also been installed. Estimates based on the tunnel's size, suggest it would have allowed approximately 2,000 KPA soldiers (one regiment) to pass through it per hour.
The second tunnel was discovered on March 19, 1975. It is of similar length to the first tunnel. It is located between below ground, but is larger than the first, approximately .
The third tunnel was discovered on October 17, 1978. Unlike the previous two, the third tunnel was discovered following a tip from a North Korean defector. This tunnel is about long and about below ground. Foreign visitors touring the South Korean DMZ may view inside this tunnel using a sloped access shaft.
A fourth tunnel was discovered on March 3, 1990 north of Haen town in the former Punchbowl battlefield. The tunnel's dimensions are 2m x 2m and it is 145m underground, the method of construction is almost identical in structure to the second and the third tunnels.
Both North and South Korea maintain "peace villages" in sight of each other's side of the DMZ. In the South, Daeseong-dong is administered under the terms of the DMZ. Villagers are classed as Republic of Korea citizens, however they are exempt from paying tax and other civic requirements such as military service.
In the North, Kijong-dong features a number of brightly painted, poured-concrete multi-story buildings and apartments with electric lighting. These features represented an unheard of level of luxury for rural Koreans, north or south, in the 1950s. The town was oriented so that the bright blue roofs and white sides of the buildings would be the most distinguishing features when viewed from the border. However scrutiny with modern telescopic lenses reveals that the buildings are mere concrete shells lacking window glass or even interior rooms, with the building lights turned on and off at set times and the empty sidewalks swept by a skeleton crew of caretakers in an effort to preserve the illusion of activity.
Until 2004, massive loudspeakers mounted on several of the buildings continuously delivered DPRK propaganda broadcasts directed towards the south as well as propaganda radio broadcasts across the border.
Within the JSA are a number of U.N. buildings called Conference Row these are used for direct talks between the two Koreas. Facing the UN buildings is DPRK's Panmungak () and ROK's Freedom House. In 1994, North Korea enlarged Panmungak by adding a third floor. In 1998, South Korea built a new Freedom House for its Red Cross staff and to possibly host reunions of families separated by the Korean War. The new building incorporated the old Freedom House Pagoda within its design.
In the 1980s, the South Korean government built a flagpole in the village of Daeseong-dong. The North Korean government responded by building a taller one — the tallest in the world at in Kijong-dong.
The "Korean wall" is a concrete barrier that was allegedly built along the length of the DMZ in South Korea between 1977 and 1979. Dutch journalist and filmmaker Peter Tetteroo shows footage of what he believes (at the prompting of his North Korean guides) to be the Korean Wall. North Korea contends:
In the area south of the Military Demarcation Line, which cuts across our country at its waist, there is a concrete wall which [...] stretches more than from east to west, is high, thick at the bottom, and wide in the upper part. It is set with wire entanglements and dotted with gun embrasures, look-outs and varieties of military establishments [...] the South Korean rulers built this wall over a period of many years from 1977.
In December 1999, Chu Chang Jun, North Korea's longtime ambassador to China, repeated claims that a "wall" divided Korea. He said the south side of the wall is packed with soil, which permits access to the top of the wall and makes it effectively invisible from the south side. He also claimed that it served as a bridgehead for any northward invasion. One clarification in 2007, from an assistant of Mr. Cho at the Korean embassy in WDC, that this is mostly, or at least partly, an artificial cliff cut into the north side of the terrain, and explains this combination semantic and 'blind-men & elephant' issue. At the security passage between the North & South, it is easy to manage the contours and make the cliff invisible from the limited points of view allowed within the security compound. None of the plausible descriptions from the North, South, or USA, contradicts this explanation of the appearance or function of this at least partly one-sided wall.
According to the United States, the wall does not exist, although there are anti-tank barriers along some sections of the DMZ.
Panmunjeom is the site where the negotiations that ended the Korean War took place. It is the main centre of human activity in the DMZ today. The village is located on the main highway and near a railroad connecting the two Koreas.
The railway, which connects Seoul and Pyongyang, was called the Gyeongui Line before Korea was divided in the 1940s. Currently the South uses the original name, but the North refers to the route as the P'yŏngbu Line. Today, the railway is mainly used to carry materials to the industrial complexes at Kaesong. South Korea workers also use it to commute there. When it was reopened in the early 2000s, this was seen as a sign that the relations between both countries were improving. However in November 2008 North Korean authorities closed the railway because of growing tensions with the South. When former South-Korean president Kim Dae-jung had died, a delegation from North Korea also attended his funeral. On that occasion, talks were held with South Korean officials. In September 2009, the Kaesong rail and road crossings were reopened.
The road at Panmunjeom, which was known historically as "Highway One" in the South, was originally the only access point between the two countries on the Korean Peninsula. Passage is comparable to the strict movements that occurred at Checkpoint Charlie in Berlin at the height of the Cold War. Both North and South Korea's roads end in the Joint Security Area; neither highway meets because there is a concrete line that divides the entire site. People given the permission to cross this border must do so on foot before continuing their journey by road.