Most roller coasters put their stomach-dropping slopes and brain-twisting loops front and center for all the world to see. But the amusement-park attractions known as “dark rides” keep their thrills hidden. As you’re standing in line for a tour of a haunted house full of ghosts and ghouls, a high-seas adventure with pirates, or a ride on the range with gun-slinging cowboys of the Wild West, all you can see are the riders in front of you, who get into little cars before disappearing through swinging doors into the dark. You hear the sounds of screams and shrieks coming from within. And then, an empty car arrives, stopping before you with a mechanical ka-thunk. You’re next.