Andros is the closest of the Cyclades to Athens, which is exactly why it works so well for a weekend away: a mountainous, green island of walking trails and quiet beaches that you can reach and leave without a long day at sea. The ferry back to Rafina is how almost everyone returns to the mainland.
You leave from Gavrio, the island's main port on the north-west coast, a working harbour village about 30 km from Chora, the capital. The boat lands in Rafina, a seaside town on the east coast of Attica, about 30 km from central Athens and much closer to Athens airport than Piraeus. For travellers flying out, that geography is the main reason to use this route.
Because the crossing is short and runs daily all year, Andros works well at either end of a trip: as a gentle first stop before Tinos and Mykonos, or as a last few days of walking and swimming before your flight. Many people also combine it with Tinos, which is only a short hop south.
The main choice is speed versus price and comfort. The fast boats are quick but run mainly from spring to autumn. The conventional ships take closer to two hours, carry cars and run every day of the year. Ferryhopper warns that tickets on this route sell out quickly in summer, so book about a month ahead for July and August, and earlier with a car.