Three-dimensional gravity has no local degrees of freedom, yet its physics is far from trivial: everything interesting lives on boundaries and corners, where gauge symmetries become physical and edge modes appear. The same mechanism governs the quantum Hall effect, whose bulk is described by a Chern-Simons theory and whose edges carry chiral currents. This project explores new corner structures and their symmetry algebras in 2+1 gravity, including its non-relativistic (Newton-Cartan) and Carrollian limits, and uses them to build a precise dictionary with Hall effect models, from edge states to Hall viscosity.