There is a compelling connection between equations of gravity near the black-hole horizon and fluid-equations. The correspondence suggests a novel way to unearth microscopic degrees of freedom of the event horizons. In this work, we construct a microscopic model of the horizon-fluid of a 4-D asymptotically flat, quasi-stationary, Einstein black-holes. We demand that the microscopic model satisfies two requirements: First, the model should incorporate the near-horizon symmetries (S1 diffeomorphism) of a stationary black-hole. Second, the model possesses a mass gap. We show that the Eight-vertex Baxter model satisfies both the requirements. In the continuum limit, the Eight-vertex Baxter model is a massive free Fermion theory that is integrable with an infinite number of conserved charges. We show that this microscopic model explains the origin of the macroscopic properties of the horizon-fluid like bulk viscosity. Finally, we connect this model with Damours analysis and determine the mass-gap in the microscopic model.
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