I've been there probably 6 times back in the late 80's and early 90's... it's a magical place and when i went there i was with a group of college students from Lima, so all safe, however i witnesed A LOT of crazy shit in plain daylight. In San Pedro de Casta, the little village where you get on bus from Chosica (1hr from Lima) you can get the mules to go up the mountain, you can also get one of the villagers as your guide for some $$$$... you'll also need to hire someone from there to bring you water as there's nothing up there... from San Pedro (5hrs from Lima in bus) to the "meseta" (the first camping spot) it's like 8hrs hiking up hill... to the "fortaleza" is a total of 10-12hrs... plan accordingly and make sure you're in great shape and health. The closest medical help you'll get is 5hrs away.... now this was back on the day, i'm assuming things have change a bit but that is still a place very hard to reach. I can get you more details if you want me to...