Why everyone says do a boat tour
Santorini is the rim of a flooded volcano, and from land you only ever see half the story. Get out on the water and the whole shape of the caldera opens up — the layered cliffs, the white villages stacked along the top, the dark volcanic islets in the middle of the bay. It is, genuinely, the thing most people remember most from their trip.
Almost every tour follows a similar loop: sail past the caldera cliffs, anchor near the volcanic hot springs for a swim, stop at a couple of coloured beaches you can't reach by road, and time the return for sunset. The difference between a good day and a forgettable one is not the route — it's the boat, the group size and the crew. Choose a smaller, well-run catamaran and you'll have space, shade and a proper meal. Choose the cheapest big boat and you'll be one of eighty people queuing for the same ladder.
Book a tour that includes the sunset, but board in the afternoon. You get the swimming and the hot springs in daylight, then the famous sunset from the water — far calmer than fighting for a spot in Oia.