In Poland: At Chelmno, Hitler’s first death camp, as many as 350,000 people were killed, many in vans that pumped in carbon monoxide from captured Soviet tanks.

Sometimes during quiet moments I glimpse a shadowy blur. It’s gone as fast as it’s there. But it’s there. Occasionally what follows is a faint odor I now know well: the smell of death. At nearly every camp we visit, the smell still lingers, even 70 years after it operated as hell on earth, even if there’s a thick blanket of snow on the ground (but especially if there’s not a blanket of snow on the ground.)

Am I seeing spirits? Maybe. Perhaps I’m just having sensory hallucinations. Either way, this much is certain: I’ll be haunted by what I’ve been witnessing.