Greece - Meteora

"In a region of almost inaccessible sandstone peaks, monks settled on these 'columns of the sky' from the 11th century onwards. Twenty-four of these monasteries were built, despite incredible difficulties, at the time of the great revival of the eremetic ideal in the 15th century. Their 16th-century frescoes mark a key stage in the development of post-Byzantine painting." 

Source: UNESCO World Heritage