You really need more than 4 hours in Santorini. It really is a beautiful place. The island is volcanic and the city of Fiere sits high up on a cliff. From the Old Port you can walk which I would not recommend in the heat, you can take a donkey ride which is kind of stinky but everything you have seen in the movies, or you can take the gondola ride up. Be prepared to wait when two ships dock at the same time. Actually, the ferry you from the ship first because there is not dock. We enjoyed a very tasty Gyro and the views. Also, the roads in Santorini are not made for strollers.