Halkidiki is a three-pronged peninsula southeast of Thessaloniki, and the closest thing northern Greece has to the island beach experience without actually getting on a ferry. Three long fingers of land -- Kassandra, Sithonia, and Athos -- reach south into the Aegean, each with a distinct character.
Kassandra, the westernmost, is the most developed and easiest to reach from Thessaloniki (about 90 minutes). It has long sandy beaches, resorts, and a lively summer nightlife scene. Sithonia, the middle peninsula, is quieter and greener, with pine forests running down to turquoise coves like Karydi and Kavourotrypes -- it feels more like an island. Camping on the beach is still common here, though the best spots fill up in August.
Mount Athos, the eastern peninsula, is an autonomous monastic republic that has been continuously inhabited by Orthodox monks for over a thousand years. Access is restricted: only male visitors with a special permit (the diamonitirion) are allowed in, limited to about 100 per day. Even from the sea, on a cruise from Ouranoupoli, the sight of Byzantine monasteries perched on cliffs above the water is extraordinary.
The mainland part of Halkidiki, behind the three peninsulas, is hilly and wooded, with the ancient site of Stagira -- birthplace of Aristotle -- near the coast, the well-preserved Hellenistic town at Olynthus, and the unusually rich Petralona Cave inland.