The Iron Triangle (Hangul/Hanja/Romanization: 철의삼각/鐵의 三角/Cheor-ui Samgak) was a key communist Chinese and North Korean concentration area and communications junction during the Korean War, located in the central sector between Cheorwon and Gimhwa-eup in the south and Pyeonggang in the north. The area was located 20 to 30 miles (30 to 50 kilometres) above the 38th parallel in the diagonal corridor dividing the Taebaek Mountains into northern and southern ranges and contained the major road and rail links between the port of Wonsan in the northeast and Seoul in the southwest.
During the war the area was the scene of heavy fighting between the Chinese People's Volunteer Army and the US Eighth Army during the Battle of White Horse (Baengmagoji/백마고지) and the Battle of Triangle Hill in October–November 1952. The Battle of Pork Chop Hill in March–July 1953 took place to the west of the Iron Triangle. This complex was eventually named the "Iron Triangle" by newsmen searching for a dramatic term. Today, the region straddles the Demilitarized Zone.
This area had the highest number of casualties during the Korean War with the Battle of White Horse and Battle of Mount Oseong. The Iron Triangle Battlefield was prohibited to the public after 1953 when the war ended in a ceasefire. Yet the reality of the war only began surfacing from November 1989.
The Iron Triangle Battlefield was the headquarters and frontline of the North Korean Army. This area had the unique natural advantage of being a difficult target for Allied forces to attack, but remained an easy area for North Koreans to defend. At the old battlefields are the labor headquarters, the 2nd tunnel and the remains of a train with a sign that reads 'The iron horse wants to run'. The Labor Headquarters, a Russian-style 3-story building, was built by compulsory fund raising and labor mobilization. Many people who were here during the anticommunist movement were later tortured and killed. Behind the building remains of people, bullets and iron chains can still be found even to this day.
This is also the area where the 2nd tunnel, 108km north from Seoul, was made by North Koreans who were planning to invade South Korea. It is also known as the gathering area of seasonal birds and is a popular bird watching spot.