Today is a monumental occasion: International Day for Monuments and Sites. Also called World Heritage Day, the event aims to highlight how important the task of conserving our cultural heritage is. A monument can be anything from an architectural work to a sculpture—something that has outstanding value from a historical, artistic or scientific point of view. 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, these fortifications have a perimeter of over 2,438 metres. When they were first built, they served to defend the city against attacks from outsiders; nowadays, visitors can walk around nearly half of the circumference of the walls, enjoying views of the city and the surrounding countryside.