For me, i am travelling most of (western) europe.. over a course of about 4 months..about 23 different cities.. So from what ive read, a Global pass would be best? Does the "21 day" pass mean you use it 21 different days within any certain period of time? or 21 consecutive days?.. Would it be cheaper for me to do 2x "10 days in 2 months" passes? I really dont understand which pass to get...???