Santorini has got an international airport and so there are flights from Athens and from several cities in Europe. The easiest option would therefore be to arrive in Santorini bij plane.
Fly to almost any Greek island with - Aegean Airlines or - Olympic Air.
The journey by ferry from Piraeus takes quite some time but it is also possible to take a fast ferry from Crete or combine Santorini with one or more other islands in the Cyclades thus cutting the trip by sea into smaller parts.

For ferries to and from Santorini (check: Thira) or to order a ferry ticket - click here.