See how many Ferry Routes you can choose!
By the way, in Greece the ferry tickets are one price regardless where you buy. The prices are determined by the government at the beginning of each year, at least that is how it was done in the past when we used the Greek ferry services.
It is not Holiday. It is Transportation thru the Ocean to various islands / mainland. They are regular ferry services but the ferry vessels are very big, with all the facilities.
Not just in Greece, but you can also find such ferry services between Sweden / Finland and Latvoa / Estonia.
On overnight sailing there are cabins available but you can also just buy the "airline style" seats.
You really need to open your 眼界 不要您現有的知識局限