OK, the idea of enjoying amusement-park thrills at the site of a former nuclear plant may not be your idea of good, clean fun — but hear us out. The German government actually never opened its state-of-the art plant in Kalkar after it began construction in the 1970s. (The Three Mile Island and Chernobyl disasters changed their plans.) A Dutch investor bought the site in the 1990s and converted its acres of concrete and buildings into an amusement park resort. The crowning jewel is a 130-foot climbing wall on the outside of the former cooling tower and a death-defying swing ride inside.