If you have time to visit Siem Reap, you should visit Wat Thmey, a place famous for killing fields. It is a memorial site and it has different styles in the area. There are English posters so you can learn about history and the Khmer Rouge regime. I never thought there was a small killing field in Siem Reap. I visited this place as part of a city tour. No admission fees are required. There is a Polpot-era monument with bones from the big-scale massacres. When I visited here during the Khmer New Year, there was also a memorial. I also witnessed the handouts and offerings of children's monks. If you don't get the chance to see the real killing field in Phnom Penh, this is a great place to replace it.