This giant sand dune in southern Spain is about 98 feet high and 656 feet wide, making it one of Europe's largest sand dunes. What is perhaps even more fascinating is what hides beneath it.

An curved arrow pointing right. For under $30 per person you can slide down epic sand dunes in Huacachina, Peru. Story and editing by Jeremy Dreyfuss Follow INSIDER Travel on Facebook Follow ...

This story appears in the November 2012 issue of National Geographic magazine. I got my first lesson in the physics of sand dunes in 1998 on an expedition into the Sahara. In order to take aerial ...