Wouldn’t it be awesome to have a microscope which allows scientists to map atomic details of viruses, film chemical reactions, or study the processes in the interior of planets? Well, we’ve just built one in Hamburg. It’s not table-top, though: 1 billion Euro and a 3km long tunnel is needed for such a ‘free electron laser’, also called 4th generation synchrotron light source. I will talk about the basic physics and astonishing facts and figures of the operation and application of these types of particle accelerators.