best beach in Athens

Athens proper has no beaches. I think if you want options at the shore, you could do a couple things as a day trip.

• Head down to the port at Pireaus (Metro lines or Bus goes there) and take a ferry to one of the Saronic Gulf islands, Aegina or Poros for example, and do beach there.
• Head to one of the beaches near Athens, many accessible by bus, but Taxi might be easier (Uber has problems in Greece) here is a decent article that focuses on beaches with easy access: http://www.greece-is.com/athens-riviera-10-of-the-best-beaches-in-attica/

You might have a look at Glyfada, right on the water and a suburb of Athens. We stayed there one year to attend a conference. There is public transportation into Athens.

Athens has nice beaches, where you can swim in crystal waters, sunbathe under the warm sun and do water sports. Most beaches around Athens are organised with sunbeds and water sports facilities, and the impressive thing is that you are so close to Athens and you can go there by tram in less than half an hour! Check out Faliro and Alimos. If you want to get a bit further Glyfada, Voula, Vouliagmeni are some other choices. You can also get to places like Schinias, Porto Rafti, Lagonisi, Sounio these can be reached by bus, about 1 hour from Athens. Personally when I cannot leave Athens I prefer to get to Schinias (Karavi or Pirates De Cuba are great beach bars) or Porto Rafti (there is an awesome beach in the area called Avlaki)

You could also get to the Saronic Islands. Located in a very close distance to Athens (half an hour - 2 hours by ferry), the islands of the Saronic Gulf give you the possibility to combine urban and seaside vacation. (Aegina, Spetses, Poros, Hydra, Agistri)