In 1974, the South Korean army discovered a major tunnel running under the southern sector of the DMZ. What came to be called the First Infiltration Tunnel was destroyed by a bomb blast (and two members of the United Nations command were killed). But soon after, the Second Infiltration Tunnel, twice as wide as the first, was discovered, in March 1975. Measuring about 2m (6 1/2 ft.) high and over 2m (6 3/4 ft.) wide, it is located in the middle of the DMZ, about 13km (8 miles) north of Jorwon. It has three exits. It is actually located in Gangwon-do, but is sometimes included in tours of the DMZ and Panmunjeom -- in fact, you can visit only if you're part of a tour group.