By Elisabeth Deffner
Climbing to the top of the Seven Summits - the highest peak on each continent - is unquestionably difficult. That's why fewer than 200 people have ever done it. Harder, still, is climbing to the top of the Seven Summits without being able to see - at all. That's why only one person, Erik Weihenmayer - a 39-year-old resident of Golden, Colorado, who was born legally blind and lost his vision completely at age 13 - has ever done it.