James Bond, 'Game of Thrones' were here: Tour the breathtaking monasteries of Meteora - CNET

In other words, don't be a jerk. Other signs said men had to wear pants, and women had to be in skirts. Most men were in shorts (it was over 90f/30c) and that seemed fine. Women, however, were asked to put on shawls (available for free at the entrance) and either fashion a skirt or shawl depending on what they were wearing.