My son was wondering can you simply get up and fly to any country? I know the State Department posts warnings of going to certain countries, but does anything actually stop you? OK, one is limited by where the commercial airlines will fly. And, showing your passport after landing in a hostile country may bring one trouble. But, let say one wanted to fly to China or Australia.* Do you need special permission to enter? How does one find out such details before one flies?
*I once heard from a friend Australia requires a visa even for visitors. How does one find this out in the first place? And, how does one find the steps one must complete to apply?