A pinhole camera is probably the simplest form of camera.
It features a light tight box with sensitive material on one side (usually photographic paper or film) and a pinhole on the other side.
Exposure is taken pointing the camera to a subject and unblinding the pinhole. After a certain amount of time (either a guess or a calculation), the blind is put back on and the camera must be taken to a completely dark place to extract the light sensitive material and develop the image.