Travel and the freedom of movement are some of the great equalizers in the world. It allows people to discover different cultures, to learn about exotic places and grasp the grand scheme of Earth's entwined ecology. But as we explore the Earth, we must remember to tread lightly. Tourism is good for people, but it isn't always good for the landscape. Some of the most beautiful places in the world are being marred by too many visitors. Here's our list of the top 15 travel destinations being ruined by tourism.