Angkor Wat is an ancient city in Cambodia that was the center of the Khmer empire that once ruled most of Southeast Asia. This cilvilazation went extinct, but not before building amazing temples and buildings that were reclaimed by the jungle for hundreds of years. Though this place is packed with tourists, it’s still breathtaking to see. The most popular temples are Angkor Wat, Bayon, Ta Phrom, and Angkor Thom. I would recommend getting a multi-day pass so you can visit some of the outer temples where there are less crowds. The closest major city and launching pad for tours here is Siem Reap. This travel guide to Angkor Wat has information about the temples and transportation.