These pictures reveal the inside of invasion tunnels dug by North Korea — which Kim Jong Un could use to send as many as 30,000 troops an hour to the South in a stealth attack.
Fears have been raised that as many as 84 secret war tunnels have been built, with some boasting sleeping areas, a railway and enough space to move tanks.
The existence of these sprawling tunnels has raised the risk of a surprise invasion amid heightened tensions between the North and South.
The first major tunnel, which stretches 2.1 miles in length, was discovered in November 1974.
It was found northeast of Korangpo in the Korean Demilitarized Zone (DMZ), extending 1 kilometer (1,100 yards) past the official border.
The tunnel, which is 3.9 feet high and 3.2 feet wide, is reinforced with concrete slabs.
The tunnel has the capacity to move one regiment an hour — which means between 10,000 and 30,000 elite soldiers could pour through the cramped space.
It was equipped with a narrow-gauge railway and rail cars and was lit with lamps connected to 220-volt power lines.
A second tunnel was found in March 1975, 8 miles north of Chorwon, which stretched half a mile south of the heavily fortified border.
Twice as wide as the first tunnel, it is large enough to send through heavy weapons, tanks and field artillery.
Troops would be able to march through the underground tunnel at three to four abreast — meaning thousands could be deployed in an hour.
The second tunnel ran for 2.1 miles at a depth of 525 feet and is it understood to be 7.2 feet wide.
A third tunnel was uncovered after a tipoff from North Korean defector Kim Bu-seong on Oct. 17, 1978.
It runs for 3.7 miles, some 239 feet below the surface, just south of Panmunjeom.
After it was built, coal dust was smeared around the entrance so it would look like an abandoned coal mine.
It is now blocked by three concrete walls — but still has enough room to transport 30,000 troops per hour.
Another tunnel was discovered in March 1990 that runs for 3,451 feet.
The Daily Star reported that the South Korean government believes there could be 16 more undiscovered tunnels.
A retired South Korean general has previously claimed there were as many as 84 tunnels beneath the border.
But the South dismissed the claims made by Hahn Sung-chu, a former two-star general, saying they were “groundless.”
Traveling through similar tunnels that exist between the United States and Mexico is a terrifying experience: