Thanks for all the useful hints. I'm usually quite an independent traveller, but for this part of the trip, we decided finally to take a tour, basically because we have only a very limited number of days available and are not flexible on the dates. We valued a lost day higher than the additional cost for a tour guide. But as this might not be the last time going there, I'm quite sure next time (with a different time planning), we would do something more on our own. We'll see.