Square du Temple
Time Out says
Once an enormous space reserved for the Knight's Templar in the 13th century, on which they built a palace in 1667. Turned into a prison during the French Revolution, this was where Louis XVI and the Dauphin Louis XVII were incarcerated before their executions. Later a convent, then a barracks, the building was destroyed in 1857 as part of Haussman's reimaging of Paris's architecture. Today the botantic garden contains 70 species of trees, some of them quite exotic. On the main lawn, a plaque with the names of 85 Jewish children from the 3rd arrondissement who were deported to Auschwitz.