Advances in the control of light propagation and photon-photon interactions have lead to a new notion of photonic materials—states of light that resemble material systems. The greater tendency for light to leave a system, combined with the ability to coherently inject light with a precise frequency and spatial mode, leads photonic materials to operate as driven, open systems. Driven photonic systems can reach steady states that resemble the equilibrium states of thermal systems, providing a route to prepare strongly-correlated many-body states of light. Such correlated photonic states will enable new insights into non-equilibrium many-body physics as well as potential applications to metrology and quantum computation. I will describe our experimental approach to photonic materials, in which we use a degenerate non-planar optical resonator to realize a two-dimensional photon gas with an effective magnetic field, and induce photon-photon interactions by hybridizing the photons with atomic Rydberg excitations. We observe photonic Landau levels indicating a strong effective magnetic field, in addition to a singularity of spatial curvature arising from the effectively conical geometry of our photon gas. Spatial curvature provides a novel probe of quantum Hall states, which we hope to employ in future work on fraction quantum Hall states of light in this system.