There are many ways to identify beaches: sand or pebble, organized or free, far or near, accessible by road or just boat, shallow or deep, warm or cold, color of the water… you name it! Heraklion has all the above and then some.

Every trip needs a base, and for this article I will assume that you stay either in the city of Heraklion, or somewhere near it. There are options as close as a 10-minute walk or as far as one and a half hour drive away, so depending on you travel preference, you can always find an excellent beach to enjoy.
I will tell you about some of my personal favorite beaches, ordered by distance from Heraklion city, starting from the east side, that is dominated by large sand areas.
Karteros

Starting with the closest one that really is something, I will recommend the whole area or Karteros. It is reachable even by the city bus, 15 minutes away from the city center. It is a wide sand beach that includes a lot of beach bars, like “Yiampanaki”, or the municipal beach, an abandoned motel(!) from the 70s called Xenia and a lot of empty space.
Arina
Next to Karteros, there is a rocky area and then another very wide sand beach, that happens to be one of my favorites. It has many names but lately it is known as just “Arina”, after the hotel that is located next to it. On its first half, you can find a lot of beach bars, beach-volley courts, water sports (like sup) and even a canteen. On the second half it is empty and free of sunbeds. The water is very shallow and wavy.
On the other side of the city, to the west, you will find the Agia Pelagia peninsula. This includes a lot of small and narrow beaches with beautiful colored and deep waters. The area is generally protected from the northern winds and therefore has calm waters. Perhaps this is why the area is regarded as more family friendly. Most of the beaches here are surrounded by traditional restaurants and small shops.
Palaiokastro

Although it is not the best in the list, it has some unique features that make it worth visiting: There are two man made structures that make it unique. A land bridge stretches right above the beach that makes the setting look very strange. And on the cliff on the edge of the beach lies a medieval castle, built in the 16th century by the Venetians. You can visit the castle, yet the access is not through the beach, but from the main road above it.
Psaromoura

One of the most beautiful beaches in the list. It literally means “fish face”. It is small and crowded, so make sure you get there early. It offers a canteen, sun beds and a lifeguard tower. It has crystal clear waters and a rock that forms something like an in-the-sea cave. There is a traditional boat that harbors there, completing the picturesque setting.
Agia Pelagia and Ligaria

Two very similar beaches, next to each other, that are both parts of villages. They are very narrow, with excellent choices of restaurants and caffes right above them. There are a lot of families that spent the whole summer there, returning every year. Both are well protected and therefore have minimal waves. There are a lot of sea activities, like snorkeling!
Moving again to the east, towards the famous Malia and Hersonissos areas, we can find a few excellent beaches, mostly with sand and rocks.
Gouves
A former US airforce base, that now hosts the Cretaquarium, Dinosauria, a few restaurants and also… a beach. Not much of a swimming area, yet there are a lot of options for activities around it. It is quite popular among photographers, as the old buildings of the base offer a great setting for portraits.
Limanakia
Closer to Hersonissos, you will find a complex of many small beaches, with a mix of sand and rock. Very clear and calm waters make this area ideal even on the windiest days. There are a lot of diving centers and some of the best fish restaurants of the area, yet they are generally not organized.
Malia archeological site

Yes, you can swim right next to an ancient palace and combine a visit to the archeological site with a relaxing day at the beach. This beach is the delta of a small river, with beautiful sand. It is wide enough to include sun beds, a lifeguard tower and extra free space.
The south part of the Heraklion province provides access to the Libean sea, that has colder yet calmer waters. It is generally less organized and offers a mix of easy to access and very hard to access beaches.
Komos
The beach stretches for more than 2 kilometers! All of it is sand, with clear and wavy waters, looking to the west. The sunset there is just magical. At the lowest part, there is a beach bar, an archeological site (right on the beach itself!) and the most famous church for weddings in the area. The cliff on its side has tunnels made by the Germans in the second world war and is now used as a house!
Matala

Made famous by the hippies that lived in the caves on the cliff next to the beach in the 70s, this is the easiest to access in the area. Quite beautiful and unique, it is a busy and comfortable beach. All Cretans, or perhaps all Greeks, know about it!
Keratokampos
A family-oriented area, with a lovely small village and a nice beach. The surprise here is that you can combine a relaxing day at the beach, with a visit to the local modern art museum.
Agiofaragko
Probably the most difficult to access in this list, yet my personal favorite. To get there, you need to drive for 3km in a not-so-easy dirt road and then walk 20 minutes inside a beautiful gorge. The surrounding cliffs are full of half-wild goats, and their bells echo in the canyon, adding even more magic to the area. Surely an experience different than the average beach day! This was an area where hermit monks used to live, thus its name that means “Holy canyon”. You can always get there by boat, yet that way you will miss the fun.

Of course, this list is not complete. It is merely a list of my own selection, just in Heraklion. The whole island has countless small or big beaches to explore and enjoy. I recommend you do what Cretans (including me) do: enjoy each beach you can access to the maximum, always wearing sunscreen, a hat, and your sunglasses. And remember to leave behind nothing but your footsteps!