It doesn’t sound like a vacation.

The names invoke a sense of darkness and despair.

Treblinka. Belzec. Sobibor. Majanek. The extermination camps of the Holocaust.

Even as someone who has studied the Holocaust for years and knows the history well, these remained vague places, somewhere far away in the forests of eastern Poland.

But as the son of Holocaust survivors, with relatives who perished in each of these camps, I wanted to know more. I wanted to see them, walk through them. I also knew that unlike some of the more notorious camps, such as Auschwitz, few people visited these, and I wanted to go to honor the victims. So in May of this year I got on a plane and headed across the Atlantic, to visit the sites of the Holocaust.

The trip began in Berlin, where much of the Holocaust was planned and organized. From there it was a five-hour train ride to Warsaw, where I picked up a car. I headed west to Lodz, which had the largest ghetto in Europe after Warsaw. The ghettos were walled-off areas of cities where the Nazis forced the Jews to live. Unlike the Warsaw ghetto, which was destroyed during the uprising, much of the Lodz ghetto still survives and I was able to walk its streets, imagining what it had been like 70 years earlier. The Lodz Ghetto was notorious for its leader, Chaim Rumkowski, known as “King Chaim,” who had the idea that if he cooperated with the Nazis, including assisting in deportations, they would view Lodz as useful and people would survive. He was wrong. Almost everyone (including King Chaim) was eventually deported and murdered.

While the Nazis had literally thousands of concentration camps, only six of those camps were extermination camps, where the vast majority of people were murdered immediately upon arrival. Chelmno was the first of these. Unlike the later ones, there was no real camp. Jews were brought to a building in the village of Chelmno, where they were “processed” (forced to undress and their belongings taken) then loaded into large vans in which the exhaust gas was fed into the passenger area. The vans drove a few kilometers to a field outside of town. By the time the vans got there, everyone inside was dead. The bodies were buried in mass graves at a site that is now a memorial. I drove along the same narrow road, through the woods, to visit the site where 360,000 bodies are buried. I was the only person there that morning.

My next stop was Treblinka, the deadliest extermination camp after Auschwitz, where more than 800,000 Jews were murdered. Treblinka was established in the spring of 1942 as part of Aktion Reinhard (Operation Reinhard), the Nazis’ plan to exterminate Poland’s 3 million Jews. By late 1943, they had essentially completed this goal. The other two Aktion Reinhard camps were Belzec and Sobibor (by the time Auschwitz was running at full capacity in mid-1943, most of Poland’s Jews were already dead). At the three Aktion Reinhard camps there were no “selections” for forced labor; they were death factories where everyone who arrived was immediately killed.

People often wonder why more Jewish people didn’t resist. But many did. The most famous example is the Warsaw Ghetto uprising. But both the Treblinka and Sobibor extermination camps were closed after prisoners rebelled. And there were the partisans. Groups of Jews went and lived in the forests, fighting the Germans when they could. I read about one such group that lived in the Parczew forest in southeast Poland. I drove there to get a sense of what it was like. It was a forest, very thick in parts. I walked around the dense mosquito-infested forest a bit. That whole groups of people survived there, often living in underground holes, I found amazing.

As I drove through the small villages, I knew that at one point many of them had large percentages of Jews. Others had been almost all Jewish. I could see, among the new houses, old brown wooden houses that are how I imagine the Shetls (Jewish villages) looked.

My next stops were at Belzec and Sobibor, the other two Aktion Reinhard camps. Why is Belzec, the third most deadly extermination camp, so unknown? One reason is that there was almost no one left to tell about it: Of the estimated 500,000 people sent there to be murdered, only a few survived.

Both camps were similar to Treblinka in layout and function. Both were very small, in the woods, along major rail lines. Both are very close to the present Ukrainian border. But the two camps today are very different in appearance. Belzec is basically one large memorial; the whole area of the camp has been covered with what looks like volcanic stone. It lies on a sloped hill, and a giant slash cuts through the hill, following the path the prisoners took from the trains to the gas chambers.

Sobibor, the site of an uprising and mass escape by the prisoners, has been left in much more of a natural wooded state. Monuments are minimal. The path to the gas chambers is lined with newly planted pine trees, each with a plaque remembering one person or family who died there. Signposts throughout the camp tell what was in each spot. Here again, I was the only visitor.

I was expecting to dislike the town of Zamosc. I knew it only as the place where my father’s uncle and aunt had been deported. But what I found was a beautiful Renaissance town. It was built in the late 1500s, designed by an Italian architect. Jews lived there soon after it was founded. By the late 1800s the town was close to two-thirds Jewish; at the start of World War II it was still almost half Jewish. The town is the perfect little tourist town but without the tourists. It has an old Renaissance-style square with cafés all around it, nice walking streets and good restaurants and cafés.

I love walking through medieval and Renaissance towns. It can feel like traveling back in time. But in Zamosc, I was distracted by the fact that more Jewish people should have been there, the town having been more than half Jewish before the war.

My final stop was the city of Lublin and the Madjanek camp on the edge of town. Majdanek was the best preserved of the camps I visited on this trip; unlike the other camps, it was not demolished by the Germans. A large number of the buildings are still in existence, with exhibits in many of them. The gas chambers can be seen, as can the crematoriums and barracks. The camp is huge, because it also was a work camp housing tens of thousands of prisoners.

Lublin itself is a beautiful old city that once was the center of Jewish culture and learning in eastern Poland. Europe’s largest Yeshiva (which I visited) opened there in about 1930; it is being restored. Lublin also was the headquarters for Aktion Reinhard. While the general directions and orders came from Berlin, Lublin was where the extermination was planned and administered. I walked by the building that housed the railroad offices where employees sat, making schedules, arranging how passengers could get from Warsaw to Krakow, how to keep freight moving on time, and how to get 3 million people to death camps.

The building that was the Aktion Reinhard headquarters is now a school. I went inside and saw students sitting around studying. This is where the “desk-murderers,” the bureaucrats, sat, administering the details of the Holocaust. While there are lots of plaques on the walls remembering former students and teachers of the school, I see nothing describing how the murder of 3 million people was orchestrated from this building.