Mirage

In this exhibit, the object that we saw is actually an image in space created by two concave mirrors facing each other.
The object is placed at the center of the bottom mirror. When light from a point on the object hits the top mirror, it reflects in parallel rays. These parallel rays hit the bottom mirror and reflect so that they come together and form a point located at one focal length from the bottom mirror. The image produced by the mirror is a real image, since the light that forms it actually passes through the location of the image.