The camera obscura (Latin for "darkened room") is the earliest optical device and goes back over 2500 years. The small pinhole or lens at the front of the room allows light to enter and this is then "projected" onto a screen inside the room. This differs from a camera, which projects its image onto light-sensitive material. Originally images were projected through a small hole, but from around 1550 onwards, they began to use a lens, which focused the image more clearly. Creating a camera obscura is cheap and easy, and it can be used at all levels to introduce aspects of art, science, history and technology. In this article, the author illustrates how a 2500-year-old "gadget" can bring delight to children. (Contains 4 figures.)