It's always seemed like the world's two great builders, Man and Nature, have been involved in a millennia long struggle, desperately trying to one up the other. This 'match-up' has never really been declared but you know it exists. And in trying to get one over the other, their styles have often blurred. Here are a few structures that look they could have been made by either, or even both. Can you tell which is which? Go on, have a try.
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