The spatial resolution of optical spectroscopy is limited by the wavelength of the probing light according to the diffraction limit. Several superresolution microscopic methods have been developed in order to overcome this limitation, ranging from life sciences to broadband solid-state spectroscopy. For instance, Stimulated Emission Depletion Microscopy (STED) has been awarded the Nobel Prize in Chemistry in 2014. However, this solution.based approach cannot be applied in solid-state physics, which calls for different methods. Scanning Near-Field Optical Microscopy (SNOM) is a powerful tool to measure the full optical spectrum from THz frequencies up to the visible range. Here, the resolution is limited just by the sharpness of the used AFM tip, reaching length scales down to 10 nm, orders of magnitude smaller than the wavelength of the probing photons. Different to other scanning probe techniques, SNOM is sensitive to both metallic and insulating materials and reaches several 100 unit cells below the surface, thus it truly probes the bulk of the investigated material. Recently, this method has been successfully implemented in low-temperature experiments (cryo-SNOM), establishing it as an extremely sensitive, versatile tool to study metal-insulator transitions and various other unconventional phenomena in correlated electron systems.