Arch of Reunification, Pyongyang (Photo: Wikipedia Commons)
Why it's Taboo: The militaristic single-party state is highly insular and largely closed off to the rest of the world. If you attempt to enter North Korea without the proper visa and passport, you risk arrest, long-term imprisonment, heavy fines, and forced labor. The United States does not maintain diplomatic relations with the country, and thus there is no U.S. embassy in North Korea. However, the Swedish Embassy in Pyongyang is available to help U.S. citizens traveling in the country. Tourists in the country must stay with government minders at all times, and there are strict rules about what they can photograph and see.
Why it's Still Worth Going: Nick Bonner of Koryo Group (which has been running North Korea tours for almost 20 years) says, "By visiting North Korea and interacting as much as you can, you have a positive impact on engagement. You are bringing civilians into contact with Westerners and providing job opportunities."
How to Visit: Apply for a visa through the Embassy of the Democratic People's Republic of Korea in Beijing. The best way to get to North Korea is via train from Beijing; however, American citizens are not allowed to leave North Korea on the train and must take an exit flight. Be aware that the State Department warns, "If you travel unescorted inside North Korea without explicit official authorization, North Korean security personnel may view your actions as espionage. Security personnel may also view any unauthorized attempt you make to talk to a North Korean citizen as espionage. North Korean authorities may fine or arrest you for unauthorized currency transactions, for taking unauthorized photographs, or for shopping at stores not designated for foreigners. It is a criminal act in North Korea to show disrespect to the country's current and former leaders, [Kim Jong-un], Kim Jong-il, and Kim Il-sung. Hotel rooms, telephones, and fax machines may be monitored, and personal possessions in hotel rooms may be searched. … Persons violating the laws of North Korea, even unknowingly, may be expelled, arrested, or imprisoned."
Update: There is currently a temporary suspension of tours to North Korea (a response by the government to the Ebola outbreak) but tourists are expected to be allowed back in at the beginning of 2015.