10. Aonach Eagach Ridge, Scotland
The trail along the top of this ridge is so thin, and the surrounding landscape so unruly, that once you start the hike you HAVE to finish it just to get back down without risking your life.
11. Drakensberg Traverse
This jagged, expansive stretch of terrain, with its steep cliffs and rocky outcroppings, can take the breath away – in some cases permanently.