At the end of September, me and my wife will be travelling to Crete and staying in Heraklion for several days (at the Lato), before going to Santorini. I was looking for suggestions for "must see" sites and day trips that can be taken from the Heraklion. Also, is a car rental necessary to properly explore Heraklion and the surrounding area? Is it is possible/convenient to get taxi service from Heraklion to Rethymon or to other areas of Crete and back? How hard is it to get around by car and would a GPS unit be useful? thanks.