Can anyone recommend a day cruise from Athens, or which islands are "must see"? We will be in Athens 3 days pre-cruise in early October.
I just answered a similar query on another forum -- in fact, at least 2 x a week someone asks this, so I'll just cut & paste:
Here's a wonderful photo-journal of a rewarding day-trip to Aegina -- shows everything including the kind of ferry you should take https://www.flickr.com/photos/36264706@N03/sets/72157621604646139/detail/ IF you sit on an open deck for the 1-hour trip, it's like a scenic minii-cruise! Especially nice if you can take the inbound ferry around sunset.
At least one of the directions, outbound, or inbound, you should take a conventional open-deck vessel, NOT a hydrofoill (where you are trapped inside with NO view). The easiest thing is just to go to any travel agent near your hotel (They are everywhere! in central Athens) - find out the timetable for Aegina, and buy your ticket there, the night before). From Central Athens you can get a Metro to Piraeus (takes about 30 mins), and the gate for the Aegina ferry is near the Metro terminus.