On contaminated land that is too dangerous for human life, the world’s wildest horses roam free. Across the Chernobyl exclusion zone, Przewalski’s horses — stocky, sand-colored and almost toy-like in appearance — graze in a radioactive landscape larger than Luxembourg. On April 26, 1986, an explosion at the nuclear power plant in Ukraine sent radiation across Europe and forced the evacuation of entire towns, displacing tens of thousands. It was the worst nuclear disaster in history. Four