Santorini is one of the hardest Greek islands to do well with a dog: caldera villages are saturated by 50k+ tourists/day in summer, asphalt and volcanic sand hit 50–60 °C, hotels often charge 20–40 EUR/night pet supplement, and JTR airport cabin pet slots are tight. Done right (shoulder season, inland villages, south-coast beaches, early mornings) it remains a unique experience: volcanic caldera, Cycladic villages, Minoan archaeology and PDO wines on a 76 km² island.
April–May and October are ideal: 18–24 °C, dry, sea swimmable from late May, dog-tolerant beaches uncrowded, caldera villages breathing again. Avoid July–August absolutely (30–35 °C, 50k+ daily tourists, asphalt 60 °C, dogs banned from most caldera-edge restaurants). November–March is mild but many tavernas and hotels close.
The Bronze Age Minoan town of Akrotiri buried under volcanic ash by the 1620 BC eruption, the 'Cycladic Pompeii', preserved under a protective roof since 2012. The covered exhibition interior bans dogs but the outdoor approach paths, the Red Beach cliff above and the nearby cliffs are all dog-accessible. KTEL bus from Fira (1.80 EUR, 25 min).
Greece uses the euro. Santorini is the most expensive Greek island (above Mykonos in some categories): meal 25–45 EUR, caldera-view dinner 60–110 EUR/person, mid-range pet-friendly hotel 180–350 EUR/night plus 20-40 EUR pet supplement, taxi airport to centre 20–25 EUR fixed. Pet ferry cabin Piraeus 30–50 EUR supplement, Aegean cabin pet 50 EUR per leg.