Okay kiddo, a sun lounge is like a train car that's all nice inside and has big windows so people can see outside while they ride on the train. The cool thing about a sun lounge is that it's designed to be super comfortable and relaxing, like a really fancy living room. You can sit or even lie down on big cushy chairs and couches while you watch the scenery go by outside. It's called a sun lounge because the big windows let lots of sunshine in, so it feels like you're sitting in a sunny room. Some people like to ride in a sun lounge on a train trip because it's a fun way to enjoy the journey and see things they might not normally get to see.