You can book a private transport, Bus X96, Athens Metro, taxi, rental cars to get you to your hotel or ferry.

Private Transport (recommended):

Viator offers bookable private airport pick ups for all party sizes to hotels or Pireaus Port.

Bus X96:

Goes to Piraeus Port departs from Athens Airport every 30-40 minutes. Runs 24 hours, every 30 minutes (00:05 and 00:35 every hour). The travel duration is approximately 60 minutes. Bus departure Location: Athens Airport Arrivals Terminal (between Exit 4 and 5).

Rental Cars:

Not necessary, but may be useful for getting around some of the larger islands that have more dispersed attractions, and limited or infrequent public transportation, making it difficult to explore effectively without your own vehicle. Rental cars can go on ferries for a cost which can be helpful for transporting luggage.

Viator options for booking pick-up and transport from Santorini Airport to Thira Santorini Port.

We recommend booking your ferry once your flight is confirmed. There are plenty of options to keep in mind and choosing your ferry is ultimately going to be determined by what is important to you.

SeaJets are high-speed catamarans for quick connections. BlueStar are more conventional ferries, comfortable, slower. There are plenty in between.

For reference:

Direct ferry from Athens (Pireaus) to Ios: 4 hour (SeaJets), 7 hour (BlueStar)

Direct ferry from Santorini (Thira) to Ios: 30 min - 1 hour (all)

If you are turning our day into your trip (go you), consider the eurail pass. The eurail pass is good for travel by train/ferry all across Europe for a discounted price compared to purchasing individual tickets.

Eurail offers a "Greek Islands Pass" that includes 4 ferry rides for $130. We recommend looking into this if you will be island hopping. Be aware, seat selections can have an added cost depending on booking, but still likely to be a save overall.