Iraklio is the main city of Crete. It hasn't a lot of charm and suffer of some pollution, particularly sound pollution, because of motor circulation and the nearly airport. Moreover, prices for accomodations are more expensive than on the rest of the island.
The archaeological museum is nice, and you have to visit Cnossos, at 5 km from Iraklio. (see the section archaeo).
From Iraklio, you can go to the plateau of Lassithi (you can equally go there by a very nice road from Agios Nikolaos). Surrounded by mountains, the plateau doesn't have a lot of wind turbines any more, but you won't regret to come here thanks to the landscapes.
In the south, there are two archaeological sites, Gortis and Festos (see the section archaeo).