Between Varkiza and Saronida in the vicinity of Lagonisi there are a number of beaches of different shapes and styles. This is a sandy beach with a rock shelf on the shore which usually means good snorkling. Once you get past Varkiza your bus choices are reduced. The 122 from Ellinikon Metro Station goes as far as Saronida and the KTEL from Pedeon Areas stops in Syntagma and many of the beaches along the coast all the way to Sounion. But be sure you take the bus that follows the coast road and not the airport because if you take the wrong bus you won't even see a beach or the sea until you get to Lavrion.