Metéora (Μετέωρα) is one of the largest and most important complexes of Eastern Orthodox monasteries in Greece. Although it is unknown when the monasteries of Metéora were established, as early as the 11th century AD hermit monks were believed to be living among the caves and cutouts in the rocks. 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. The Metéora is home to six monasteries (of the original 20 that were built in the early 14th century) and is included on the UNESCO World Heritage List.
Metéora is off the beaten track (far from Athens and the islands) but famous at the same time (featured in the 1981 James Bond movie "For Your Eyes Only). Either way it is well worth the minimum of 2 days you will spend on the road getting to and fro just to see the wonder of this place.
Check out the whole set - Glorious Greece.