At times, travel brings you face-to-face with some of the darkest periods of human history. A visit to Choeung Ek, the best-known memorial to the victims of the killing fields, is not particularly pleasant — its center is a Buddhist stupa with acrylic sides filled with more than 5,000 human skulls — but on a first visit to Cambodia it is somehow a necessary and unavoidable experience. The same is true of Yad Vashem, the official memorial to the Holocaust, which is located on the peaceful wooded slopes of Mount Herzl, on the western outskirts of Jerusalem. If you go to Israel, a visit seems mandatory.

Similarly, on a trip to Rwanda, even if its purpose is to view gorillas and chimpanzees, it is not possible to avoid the legacy of the 1994 genocide, during which an estimated 800,000 Tutsi were murdered by their Hutu neighbors in the course of 100 days. The Kigali Genocide Memorial is located in the pleasant neighborhood of Gasabo, close to the office of the president and most of the government ministries.

In the grounds are buried more than 250,000 victims, a number that is still increasing as more remains are discovered. The visitors center contains a series of powerful displays that try to explain the origins of the animosity between the two tribal groups, the role of politicians and propaganda in fomenting the slaughter, the unspeakable events themselves and the subsequent attempts at reconciliation and reconstruction. As at Yad Vashem, it was the pictures of the dead — taken at school, at weddings, at birthday parties — that I found most affecting. And also their ordinary belongings — shoes, shirts, pants, wallets, handbags — which somehow established a visceral connection: My mother used to have a bag not dissimilar to that one; I, too, have a shirt just like that.