Hiking: Spectacular scenery and fairly reliable weather encourage this activity, but poorly marked paths are a problem. Around Meteora and in the Zagoria and Peloponnese regions are stunning walks, while Naxos island is favoured by Germans. The islands are a safe choice since you can't travel too far from humanity. May and June are prime hiking months generally as hills are scattered with wild flowers and temperatures are comfortable.
Climbing: The mainland offers the biggest climbs, with the amazing vertical pinnacles of Meteora proving popular.
Skiing: Northern Greece has mountains and snow in excess, though most foreigners consider the Greek ski resorts to be of good value and pleasant but fairly basic. Mt Parnassus, and Mt Vermio, west of Thessaloniki are the best known.
Windsurfing: One of Europe's best windsurfing destinations due to consistent sun, wind and protected bays on the islands, boards are widely available to rent. Schools are established in some of the best locations on Lefkada, Kos, Paros, Samos, Crete and Corfu's west coast.
Sailing: endless hospitable islands, sheltered bays, good winds and sun and a huge rental selection at the right price make Greece a major sail travel haven. Skiathos has a particularly large fleet.
Snorkelling/Scuba: Snorkelling is fair, with interesting rocks and fishes particularly in evidence around Paros [Monastiri], Skopelos [Velanio] and Corfu [Paleokastritsa]. Scuba is prohibited outside recognised dive schools due to government fears of theft of underwater antiquities. Some islands that have schools are: Corfu, Skiathos, Crete, Mykonos, Paros, Rhodes, and Santorini.