I always recommend Hydra island for those that are looking for a quiet and romantic getaway. The island is very close to Athens, and very accessible by ferry boat. There are no cars allowed on the island, so it is pretty peaceful and calm. You can find mostly restaurants and stores on the island, many of which have beautiful outdoor seating and twinkly lights in the night time. I don't really recommend the beaches here, I've seen way better on other islands. It's a great place for a day trip, and some evening dinner plans.