Considering the San Giorgio Hotel in Mykonos?
A VT member wrote the following comment about visiting Mykonos:
Santorini - Mykonos Ferry by SOLODANCER
It isn't necessary to book way ahead of time - especially from where you are - your ticket to the ferry to Mykonos from Santorini. Travel agents do this all the time because this is how commissions pile up in their purse. And they do it with a sense of urgency for you and even a little injection of fear that you'd miss the ferry to your destination. Relax. There are plenty of ferry services plying regularly between the Cyclides islands and the rest of Greece. The service between Santorini-Mykonos-Santorini and the other islands are very much on a daily schedule due to these islands' popularity. What you need to do is obtain your ticket - from the ferry company itself with an office very likely in town or by going down to the docks - once you arrive in Santorini or whichever island you'd happen to be. And make sure you allow yourself a couple of hours ahead at least to be down at the pier to double check and secure your boarding. Good luck and happy trails.