A gardener waters a patch of grass at the heart of the former Navy School of Mechanics (ESMA), in downtown Buenos Aires. It’s a tiny island of greenery in a sea of asphalt and gray concrete. On the surface, it looks like an unremarkable educational facility, but just four decades ago it was a concentration camp that held thousands.

“You can feel it, wherever you go around here,” the gardener tells me. “The collective pain . . . ” He starts to finish his thought before deciding that there’s nothing more to be said.