Avlaki is one of the beaches I used to go to as a teenager because it was so close to our house in Agia Paraskevis. Back then it was just a cove with a beautiful sandy beach and a small taverna. Now there is a big parking lot, you pay admission and there are cabanas, beach chairs and fast food. But it is still a pretty nice beach, one of the best withing striking distance of Athens. If you can get a bus right there from Pedeon Areos you should be able to get to Porto Rafti or Markopoulo and take a local bus or taxi from there.