Most people who land in Heraklion treat it as a corridor: off the plane, out to Knossos, onto a beach somewhere else. That's a shame, because Crete's capital is one of the oldest continuously important places in Europe. The Minoans built their greatest palace just outside it around 1900 BC. Arab emirs founded the town itself as Chandax, "the castle of the moat", in the 820s. Venice turned it into Candia and wrapped it in walls that held out against the Ottomans for 21 years. Today it's Greece's fourth city and the biggest on any Greek island.
It's not a pretty-postcard town like Chania, and it doesn't pretend to be. It's a busy, working city with traffic and concrete, and in between are Venetian fountains, a harbor fortress, the best Minoan museum in the world and a food culture so serious that UNESCO named Heraklion a Creative City of Gastronomy. Order a raki anywhere and a plate of something will arrive with it, unasked. Five days is enough to see the city properly and still reach the south coast and the wine villages.
Day one is the Venetian center and the harbor, day two Knossos and the Archaeological Museum, day three Gortyna, Phaistos and Matala in the south, day four Archanes and the wine country, and day five the walls, the sea and a last raki. For days three and four, rent a car: the buses that go there run only a few times a day. Heraklion is also a good gateway to Greece at its most distinctive, and our piece on the culture of Crete explains why Cretans see themselves as a little apart from the rest of it.