1) Saudi Arabia
Requires all visitors to be sponsored by a legal resident or citizen. Even if you’re sponsored properly, there’s no guarantee that you’ll then be awarded a visa as the application process is highly selective.
Iran doesn’t even have an American Embassy anymore, thanks to the tense Iran hostage situation that occurred there in 1979. If you are able to secure an Iranian visa through the Pakistani embassy in Washington, D.C., you will need to show that you’re traveling with a tour group.
3) North Korea
North Korea requires all visitors to book a full package tour before visiting. During your visit, you’ll be required to stay with your guides the entire time. The lack of North Korean embassy in the U.S. means you’ll need to travel to China before booking a tour.
Syria is in the midst of conflict, but if that doesn’t deter you, the nearly impossible-to-get visa might. Since each visa has to be approved through a complex process, potential visitors face an indefinite wait to be approved or declined.
The relationship between Cuba and the United States is relaxing slightly, but the current travel regulations still don’t allow anyone looking for a a good Cuban sandwich and a Caribbean beach to book a flight. Unless you can prove that you’re in Cuba for one of the official reasons, you’ll have to wait longer to visit.