You are all most likely aware of Pol Pot and the Khmer Rouge. The consequences of this regime are still being felt today. From this genocide many of the brightest people were killed to stop any uprising and because of this massive brain-drain, once the regime ended the country had to rebuild with under educated citizens.
Some of the soldiers involved in the Khmer Rouge were put to trial and sentenced, however, some people still believe that even though they were punished, it is the locals that are still being punished more for what they and their ancestors were put through.
It is quite a scary thought that this was still very recent. After learning more about their history while in the country, I found out that the faces of the regime were out there in meetings with the UN, however, what was actually happening to their countrymen were so well hidden that the rest world wasn't aware of the devastation that was happening at the same time.
The Cambodians will not let their people forget the suffering they endured as they believe it will make them stronger. They have turned former fields used for the massacres and prisons as memorial grounds and museums to educate the younger generation and visitors wishing to know more about their culture and what makes them who they are today.
Your hostel should help you get to both the places below. We paid between the three of us about US$10 roughly each for the tuktuk driver to get us here. Although, you can haggle with other tuktuk drivers instead for a better price.
1) Choeung Ek Killing Fields Memorial / Genocide Centre
There is a small entrance fee and you get given headphones and a recorder which will narrate what happened at each stop. They come in difference languages too, otherwise you could pay for a tour guide. You will need a good two hours at least here, depending on how quickly you want to walk through the grounds.