Heraklion
Sights
The Palace of Knossos
Historical Museum of Crete
The Archaeological Museum
Venetian Fortress (Koules) of Iraklion
Museum of Cretan Ethnology
Morosini Fountain (Lion's Fountain)
Day Trips
Palace of Knossos
Personally, I don't consider this a day trip, but it quite a distance from a city, so for some it might.
Just ask your hotel where to catch the bus, about 20 minutes.
Gournia
Take a bus to Gournia, about 1 hour 40 minutes
Ammoudara Beach
Take a bus to Gournia, about 1.5 hours
Food
Cretan salad
Tabouleh Salad
Greek Salad
Gyros
Souvlaki
Grilled plates
Stuffed aubergines (eggplants)
Grilled octupus
Calamari souvlaki
Octupus salad
Anchovies
Silver Snapper
Seafood pasta
Lamb
Swordfish
Greek yogurt with honey
Fresh figs
Warm honey and Tsipuro (alcohol)
Restaurants
The Herbs' Garden