Votsalakia Beach is a small urban beach tucked between Zea and Mikrolimano, close enough to central Piraeus that it works as an easy swim rather than a beach-day expedition. The shore is pebbly and backed by the city, but the setting has its charms: marina views, cafes nearby, and the relief of getting into the water without crossing half of Attica.
Come with realistic expectations. This is not one of the great beaches of Greece, and it can be crowded in warm weather, but it is useful if you are staying in Piraeus before a ferry or want a quick local dip after sightseeing. Water shoes help on the stones.