There are several excellent options in near vicinity to Heraklion. The trip to resorts like Stalida or Agia Pelagia will take less half an hour. If you want to spend even less time on the road, then you can go to the beaches close to the city such as Amoudaria or Kokkini Hani. Some would prefer those lovely wild southern coast places like Matala, but it takes an hour or more to reach there. The best thing about Heraklion and Crete as a whole is the chance to enjoy a different beach every day.