I have been catching some of the news of the Khmer Rouge tribunal taking place now in Phnom Penh, Cambodia. Last winter, we visited a museum there commemorating the atrocities carried out in the 1970's by the Pol Pot regime. Nearly 1/4 of the population was wiped out. The museum is a somber place with signs throughout the building that say "No Laughing". Schoolchildren are forbidden to laugh or run on the grounds when they visit.
From the museum, our guide took us to the nearby "killing fields". He described what we would see and gave us the history, but refrained from entering the area, as it is still too upsetting after all these years.