Santorini is an excellent island for an exceptional holiday. One has to choose a hotel on the cliffs which provides a truly indescribable view of the caldera (a geological term for a certain shape of a volcano), which can't be captured on camera. It must be experienced. I myself have been to Santorini four times so far, and I'll certainly go there again someday. For me, there are two really stunning towns on the Santorini cliffs: Thira and Oia.
During my last visit, I was very interested in exploring Thirasia. It's an island on the opposite side of the tourist-friendly part of Santorini. Here, tourists arrive exclusively on board of ships hired for organized trips and only to the bottom area of the island with plenty of restaurants. Almost no one spends the night. I arranged a tour in an off-road vehicle with a native guide who showed me the entire Thirasia with its old monasteries, churches and old abandoned hotels. Tourism didn't take root here, God knows why.
Another thing worth mentioning are the 2000-year-old excavations in Akrotiri, a consequence of a volcanic eruption. Of course, I visited also the center of the caldera - the volcano. But it has been asleep so far - its smouldering is only minimal.