Platys Yialos used to be a swamp but has now been monopolised by back-to-back hotels lining the long sandy beach. The biggest and longest established resort on the island this is no place to look for a Greek holiday - there is not a trace of Greece to be seen here any more. A long crescent of sand is backed by low hills.
Terraced tavernas line the sands which heave with bodies in the high season. The frequent bus services from Mykonos make this the main target of day visitors, swelling the high numbers already staying here. Water sports abound as do the howling jet skis, so pack some earplugs with the sun cream. This is also the main calling point for small boats taking visitors to the other south coast beaches and to the surrounding islands, Delos in particular.
Boats for Delos though leave early, around 8am. If you want to escape the crowds Paraga is a tiny beach in a nearby bay which has a couple of very good tavernas and not much else.