Walk through a dark part of Cambodian history with a visit to the Tuol Sleng Genocide Museum (Prison S21) and the Choeung Ek Killing Fields. A convenient bus takes you to each location, where you can learn about the executions carried out by Khmer Rouge regime during its rule from 1975 to 1979.

Begin your tour in a comfortable coach as you're transported from your hotel to the Tuol Sleng Genocide Museum. When you step out into the 4-bulding complex, which was a former high school before its use as the infamous Security Prison 21, either choose to explore the museum on your own, or engage an inhouse tour guide at little cost per person, or rent an audio-guide with 15 language options. Begin walking through each building's exhibits, which detail the history of the prison that oversaw the imprisonment and torture of 17,000 people during the Khmer Rouge regime.

Continue your journey by transferring to the Choeung Ek Killing Fields. On the drive over, watch a documentary about the notorious regime that gives you further context for your visits. Upon arrival at the fields, either rent an audio-guide or venture out on your own through the largest mass grave of the Khmer Rouge's victims, where more than ten thousand people are thought to have been killed and buried. At the end of your tour, reflect on your day as you head back to your hotel in Phnom Penh.