Korea infiltration tunnels

Stretching for miles and, at times, hundreds of feet underground, three tunnels dug by North Korea underneath the Demilitarized Zone (DMZ) into South Korea are accessible via tours from the south side. Each has been blocked with concrete at the border.

• The Second Tunnel, discovered in 1975 in Cheorwon, has three exits and can accommodate tanks. Only 500 meters of the 3.5-kilometer tunnel is open. Tours, including entry to the Cheorwon Peace Observatory, cost KRW4,000 (near $4) per person. Closed Tuesday.

• The Third Tunnel, discovered in 1978 only 45 miles north of Seoul, is considered the most dangerous yet found. It is estimated 30,000 soldiers could have moved through it per hour. KRW8,700. Closed Monday.

• Within the Fourth Tunnel, found in 1990, visitors take a train ride. A war museum is on site. KRW2,500. Closed Monday.

Foreigners each need a passport to enter a tunnel. For info, visit www.dmz.go.kr/english.