If traveling in early July by ferry from Athens to the isalnds of Santorini, Paros & Naxos do we need to make reservations in advance of our arrival to Athens to make sure can get ferry reservations? Making reservations on line is so confusing - any suggestions!!
Go to www.seat61.com. It has tips for all manner of train and ferry travels in all European countries, including Greece. That site has saved us untold misery in booking trains and ferries across the UK and Europe, Asia too.
Also see http://greektravel.com/islands.htm
If you can't get advance bookings, I would not worry unduly. In my 10 visits to Greece I have never booked a ferry in advance and have never had a problem getting to my destinations as a foot passenger. With a car would be a different story.
Roger