Will be in Cuzco 6 days in August. Is it advisable to do a 3 night / 4 day trek. We would stay in Cuzco for 1 day, 4 days for trek and last day fly out early. Is this cutting things too close and not giving enough time to acclimate to the altitude? We are young (25 yo) and somewhat fit, but would exercise and get in proper shape (knowing that we have until August). Are the trek's spectacular or is going by train almost as good? I don't mind the effort (in fact, it sounds fun), and would love to see more...but have heard that the trails are run down and overused. We were looking at llama trek and peru trek (both seemed to get good reviews on here).