"Taking you to places where your mother would rather you stayed away from." That's how one Western travel agency advertises its tours to North Korea.

The U.S. government doesn't want you to go there either. Three of its citizens have been detained in the last eight months while on tourist trips to the North, including Jeffrey Fowle, a visitor from Miamisburg, Ohio, who was arrested in May.

Despite the risks, tour operators say business to North Korea is booming, albeit from a low base for one of the most isolated countries in the world. For Pyongyang, tourism is one of the few sources of the foreign currency it relies on to overcome international sanctions related to its nuclear and missile programs.