The scale of the universe.
Science and maths have never been my strengths, but this interactive scale of the universe by Cary Huang (of http://htwins.net) is incredible, down to every last detail: the fluttering hummingbird, the different kinds of quarks and the amusing descriptions for each object which will interest anyone, regardless of prior knowledge.
Visit it here. Do it now! I promise that you will be as fascinated as I was.