Ferry from Athens to Santorini?
 

What area of town is the ferry leaving from? We are staying in the Plaka area. (is it a long way to the ferries from there?)

Also, what is the name of the high speed ferries that take about 4-5 hours? Thanks

The ferries depart from the port of Pireas, which is about 15 kms from Plaka lets say. If you take a taxi it can't take you more than 40 minutes to get there (if there is traffic) so i would leave the hotel about one hour and a half earlier than the departure of the ferry. The name of the speed ferries i don't know but i am sure if you ask at any travel agency they will gladly tell you.
Kalo taxidi! (bon voyage)

wordsmith,

Ferries also leave from Rafina. Hopefully someone will come on with more info for you.

Hey i searched the ferry for you,
the fast one is HIGHSPEED 3 of the company Hellenic Seaways and the journey lasts only 5 hours (while by other ferries it will surely be above 7 and a half, even 10!).
From Rafina I didn't find any ferries going to Santorini, but to other islands of the Cyclades (Paros, Naxos, Ios, Mykonos). Again i don't think Rafina would be convenient for you, since it is much easier for you to get to Pireas from Plaka than to Rafina.

From the Plaka it will be easy and cheaper to take suburban rail line to Piraeus from the Monastiraki Metro Station. The Piraeus Station is very close to the Hellenic Seaways dock.