I am terrified of heights and not in the greatest shape, but I am so glad I climbed Huayna Picchu.
Buy your tickets as early as you can, they only allow 200 people/day to climb it. Be warned, they only take VISA on-line.
It took me about 1 1/4 hours to climb up to the top. Everyone on the way back down tells you it's only another 10 minutes to the top, it's kind of encouraging and entertaining even though they are lying through their teeth!
The view from the top is absolutely AMAZING.
Make sure you have good mobility, there are some tight squeezes and narrow ledges to navigate. Even if you don't get all the way to the top, there are some spectacular views on the way up if you're brave enough to turn around and look out. (I wasn't)
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