The detection of optical counterparts of hot spots in radio galaxies has been a challenge in astrophysics since the 1960s. Being located at several 100 kpc away from the AGN, they represent the most striking sites of interaction between the AGN ejecta and the ambient inter-galactic medium. Particle acceleration is thought to drive their emission and therefore, due to their remote locations, hot spots are the best laboratories to study the physics of that mechanism in detail. Using carefully directed selection criteria and the VLT we have discovered hot spots in the optical at an unprecedented detection rate, all of them disclosing very intriguing structure. This structure pinpoints the regions where electrons are accelerated to highly relativistic energies -- the particle accelerators. With HST we aim at resolving these accelerators for the very first time. This will enable us to establish the nature and origin of these relativistic particles in the hot spots of radio galaxies. The results of these studies not only represent a key for understanding the evolution of radio sources but also provide important input to plasma acceleration problems in general.