Most Greece itineraries include both, but if time is tight, Athens and Santorini represent the country's two headline experiences — ancient capital versus postcard island — and they deliver very different trips.
Athens is the clear draw here — The Parthenon and Erechtheion atop the Acropolis are among the most significant ancient sites on earth, backed by the excellent Acropolis Museum. Santorini's own ancient history is more niche but genuinely remarkable: Akrotiri Archaeological Site, a Minoan city preserved in volcanic ash centuries before Pompeii.
This is Santorini's whole reason for being — Oia Village's whitewashed, blue-domed houses over the caldera are one of the most photographed views in the world, and Fira Town adds a livelier cliffside base. Athens has nothing comparable; its appeal is urban and historical rather than scenic.
Santorini's Red Beach (Kokkini Paralia) and volcanic-sand coastline make it a genuine beach and relaxation destination, with boat tours around the caldera as the signature activity. Athens is a busy, hot capital city with no real beach culture of its own, better suited to intensive sightseeing than lounging.
Athens is inexpensive by European capital standards and easy to reach with direct flights worldwide. Santorini is considerably pricier — hotels with caldera views book up and cost a premium — and typically requires a connecting flight or ferry from Athens, adding a day of travel each way.
Choose Athens for ancient history, museums, and an affordable, easy-to-reach capital city trip. Choose Santorini for iconic caldera views, beaches, and a romantic or relaxation-focused getaway. Most travelers do both — Athens for two or three days, then a short flight or ferry to Santorini to unwind.