Sangsueng OP is the foremost front to observe North Korea and carried out caution duty by Biryong troops during 24 hours. It is seen many animals and plants can not see other area near this OP. Sangsueng OP is called the front line Observation because of it can be seen North Militaries’ face and motion through the telescope and be heard broadcasting toward the South Korea. The mode of the 1st Tunnel discovered on 15 Nov, 1974 is located this OP. Actually, the 1st Tunnel is inside the DMZ, where can not enter.