A 4km wide stretch of land divides North and South Korea and is a no-go area fenced off with razor wire. Thousands of soldiers rigorously patrol the area known as the DMZ, or demilitarised zone. Kristin Edge went underground within a few hundred metres of the dividing line. The award-winning journalist is in South Korea as part of a one-month Rotary-sponsored study exchange programme.
Army checkpoints dot Korea's rural landscape, with young-faced soldiers clad in camouflage uniforms, guns slung across their shoulders, checking paperwork.
It's a stark reminder that Korea is a country poised to take action to defend itself if needed.
Given recent threats by North Korean leader Kim Jong-Un, most soldiers in the South would be ready and on high alert.
As you near the DMZ frontline 106km north of Seoul, tall razor-topped wire fences appear with signs alerting people to the danger of mines.
It is not known how many mines are still left in the hills and the army is working to clear them.
There is also an increased military presence, with army barracks dotted along the side of the road and rows of tanks at the ready.
But farmers in nearby fields continue to ready the land for springtime planting of rice, seemingly unperturbed by the army action around them.
At the tunnel - named Tunnel 2 because it was the second of four discovered - soldiers keep watch, advising visitors photos are okay outside the tunnel but not to be taken inside or of the surrounding lookouts that are strategically placed on high points.
Blasts heard by two soldiers in the area alerted South Korea to the fact there may be a tunnel in 1973. Forty-five exploratory holes were dug, seven of which confirmed there was an underground tunnel. Over the next two years, a tunnel was then dug by the South Koreans to meet up with the main tunnel. Army officials believe there could be six more.
The tunnel, about 3.5km long, was wide enough so if needed three fully kitted North Korean soldiers could run shoulder to shoulder at a time. Up to 16,000 troops could move through the tunnel in an hour.
The North Koreans have denied they were responsible for the tunnel. Kitted out with a white helmet, I decide it is time to descend underground.
A series of more than 70 wooden steps takes you 50 metres underground.
Water drips from the roof and a small river runs along the edge of the cave. The top of the tunnel is in places so low I have to stoop and the helmet clatters against the low hanging rock.
As we walk along the tunnel, we get to an area that widens out and is as far as we can go. Just 300m more and we would be in North Korea.
CCTV cameras have been placed further along to monitor any underground advances the North Koreans might carry out.
South Koreans today are hopeful there will be reunification. Given the current climate, it won't be any time soon.