The Meteora is a cluster of huge sandstone rock pillars located in central Greece near the town of Kalambaka. The pillars were formed around 60 million years ago during the Paleogene period and were weathered and shaped by earthquakes into their current form rising dramatically from the surrounding plains. During the 14th century, when the region was politically unstable, Greek Orthodox monasteries were built atop the inaccessible pillars, and by the late 15th century there were 24 monasteries. Today only six monasteries still operate among the pillars, which have been designated a UNESCO World Heritage site.