are plenty of things for the active youth in Greece
Many organized beaches offer paragliding, hand-gliding, water skiing, canoeing, jet skiing and many other activities. Many hotels near beaches are also well equipped with gyms, and outdoor exercise facilities.
There are many opportunities also for mountain climbing in Epirus, Peloponnesos, Macedonia, and Crete. Climbing mount Olympus is also on the menu.
The rugged terrain of Greece is ideal for hiking. There are many hiking tours available in the mainland and in Crete.
Open camping is officially not allowed anywhere in Greece
although resourceful travelers find remote beaches where
they can pitch a tent for some care free and inexpensive
There are organized camping sites everywhere in Greece that for a reasonable price would provide you with your own spot to park (your camper, tent, or just your sleeping bag,) communal bathrooms and showers, running water, and most likely easy access to a beach. In fact I have noticed that campings are always near the best beaches of a location.