Three days is enough to experience Santorini's four defining sides: the caldera view, traditional villages, local wine, and its uniquely volcanic beaches.
Day 1: The Fira-to-Oia walking trail. Start very early (before 7 AM) to avoid the worst heat and crowds. The trail runs about 10.4 km and takes roughly 3 hours along the caldera's rim, passing through four charming villages: Fira, Firostefani, Imerovigli, and finally Oia. The view the entire way looks directly onto the volcanic crater and the deep blue sea. End your walk in Oia for the famous sunset, and look for an alternative viewpoint to the crowded Oia Castle — like the corner near the three blue domes by the church, or head down to Ammoudi Bay, where the sun sets directly into the sea away from the crowds.
Day 2: Wine tasting and Pyrgos village. Santorini is known for its unique volcanic vines, grown in the traditional "kouloura" basket-weave style that protects the grapes from wind. Visit SantoWines winery near Pyrgos for a tour and tasting with a caldera view, or choose one of the smaller family-run wineries. Afterward, wander Pyrgos itself, the island's highest village and one of its least touristy, with narrow stone lanes and an old Byzantine fortress.
Day 3: The volcanic beaches. Santorini has no traditional white sand beaches given its volcanic origins, but it makes up for it with striking beaches in unusual colors. Red Beach features dramatic red cliffs (exercise caution — rockfall is possible), Kamari is an organized, family-friendly black sand beach with Blue Flag certification, and Perissa is a longer black sand beach better suited to water sports. Rent a car or ATV to reach them, since they sit on the south and east coasts, away from Oia and Fira. Remember black sand heats up fast under midday sun, so bring beach shoes.
One final tip: book your hotel in Firostefani or Imerovigli for a caldera view at a lower price than Oia, while staying close to the walking trail.