There's a variety of reasons that countries and cities can become no-go zones. Sometimes it's because of war or a natural disaster, or the decision of a drug lord to base an international cartel there. For some countries it was a quick look at the outside world followed by a decision that they didn’t want any part of it. We’ve put together a list of the most fascinating places around the planet that were once off-limits, but are now, sometimes tentatively, open to visitors again.