Since North and South Korea never signed a peace treaty, they’re technically still at war. The Demilitarized Zone (DMZ), a roughly 2.5-mile buffer between the two countries, lies just 35 miles north of Seoul and is a must-see for visitors. Opt for a tour that also goes to the Joint Security Area (JSA), located on the United Nations command post where North and South Korea signed their armistice agreement. From there, you can gaze across the border and witness the guards on both sides staring one another down, or take a step into North Korea from within the blue conference building that straddles the two countries. Cosmojin and Panmunjom tours include a fascinating Q&A session with a North Korean defector on the bus ride to the border. Note: For security reasons, U.S. citizens must book a minimum of four days in advance.