Phnom Penh is the country's capital and is home to the infamous S21 detention camp (Tuol Sleng) where the murderous Khmer Rouge tortured and killed so many Cambodian citizens during its power. The prison is now a museum and forms a grisly but essential reminder of the country's sorry recent history. Visitors generally visit the museum before taking a trip to the Killing Fields, another site where the genocide of so many people took place.