Happy International Day for Monuments and Sites! Also called World Heritage Day, the event highlights efforts to conserve our cultural heritage. Some of the amazing heritage sites around the world include Machu Picchu in Peru and the Pyramids of Giza in Egypt. The stone structure in today's image is part of the medieval city walls of Ávila in Spain. Built between the 11th and 14th centuries to defend the city against attack, these fortifications stretch for 1.5 miles around Ávila. Nowadays, visitors can walk around sections of the walls, enjoying views of the city and the surrounding countryside.