Chan Chan Archaeological Zone

Chan Chan Archaeological Zone is the world's largest adobe city and the largest pre-Columbian city in South America, covering 20 square kilometers with nine royal compounds that once housed 60,000 people. Constructed by the Chimu Empire from 900 to 1470 AD, this adobe brick metropolis outperforms #10 Rainbow Mountain in historical significance, as Chan Chan was a capital for over 500 years while Rainbow Mountain only became known after 2015. Erosion from El Niño flooding has damaged the site so severely that UNESCO inscribed it as a World Heritage Site in 1986 and immediately placed it on the Endangered list, with preservation efforts costing an estimated $3 million annually to protect against further degradation.