If you only do one thing in Siem Reap, you have to spend a day exploring the Angkor Temples, the world’s largest temple complex, a UNESCO World Heritage Site. Home of Angkor Wat. Siem Reap and the Angkor temple complex were the center of the Khmer Empire, which existed from the 9th to the 15th centuries AD and was the most powerful empire in Southeast Asia. Before this rediscovery of this temple complex in the 19th century, Siem Reap had been a quiet village for centuries. After the Angkor temple complex opened to tourists in the early 20th century, Siem Reap’s popularity skyrocketed and is now the heartland for exploring the ancient Khmer empire. Siem Reap is quiet during the day as visitors spend their days in the temple complex, attending Khmer cooking classes, or relaxing by the pool. As the sun goes down, Siem Reap comes alive with vibrant night markets, tasty street food and pump bars that pour onto the street.