In contemporary condensed matter physics and photonics, four length scales are fundamentally interesting and intertwined: 1) Polaritonic wavelength λ in infrared (IR) and terahertz (THz) frequencies ω (e.g. plasmon, phonon, exciton, or magnon polaritons), which defines the scale of the light confinement and light-matter interaction; 2) Magnetic lengths  l_B =√(ℏ/eB)=257Å/√(B[T]), (with B the magnetic field), which defines the restricted electron motion in a B field; 3) Diffusion length D of the hot carriers at interfaces and the edges, which defines the scale of energy relaxation, and 4) Periodicities of superlattices induced by moiré engineering, which defines the energy scale of emerging quantum phases. In this talk, I will report 1) A new type of optical near-field nanoscopy technique (Landau level nanoscopy) to tackle all four above-mentioned ‘lengths’ simultaneously; 2) A new type of infrared polaritons that can be tuned via magnetic field; 3) A nanoscale probe of the many-body physics through the excitations of magnetoexcitons in graphene across the allowed and forbidden optical transitions. Our approach establishes the Landau-level nanoscopy as a versatile platform for exploring magneto-optical effects at the nanoscale. Our preliminary research also sets the stage for future spectroscopic investigations of the topological and chiral photonic phenomena in complex quantum materials using low-energy photons.