This is definetely a place i advise you and recommend you should visit while you travel to Greece. It is located in central Greece close to a village called Kalampaka which is near to Trikala.
____The Metéora in greek meaning "suspended rocks", "suspended in the air" or "in the heavens above" is one of the largest and most important complexes of Eastern Orthodox monasteries in Greece, second only to Mount Athos.
The monasteries are built on natural sandstone rock pillars, at the northwestern edge of the Plain of Thessaly near the Peneios river and Pindus Mountains, in central Greece (http://en.wikipedia.org/wiki/Meteora)_
This is a unique place all over the world as far as i believe and my suggestion is that this should be topping your lists.... as you can combine interesting activities, climbing and walking together with the magic view of these rocks wich will give you lots of vibes when you get out there.
Qualified climbers will help you to climb the rocks with safety if you are willing to test your adrenaline as there are experienced alpine clubs there. Of course you can choose to walk the traditional paths if you are more conservative.
Meteora is definately a very good place to visit! Very dramatic scenery!