Originally , it was the only connection between North and South Korea . In 2007 a Korail train crossed the DMZ to the North on the new Donghae Bukbu Line built on the east coast of Korea . Originally , it was the only connection between North and South Korea but that changed in 2007 when a Korail train crossed the DMZ to the North on the new Donghae Bukbu Line built on the east coast of Korea .