showed that the interface of a 3D Ising model with minus boundary conditions above the xy-plane and plus below is rigid (has O(1)-fluctuations) at every sufficiently low temperature. Since then, basic features of this interface-such as the asymptotics of its maximum-were only identified in more tractable random surface models that approximate the Ising interface at low temperatures, e.g., for the (2+1)D Solid-On-Solid model. Here we study the large deviations of the interface of the 3D Ising model in a cube of side-length n with Dobrushin's boundary conditions, and in particular obtain a law of large numbers for Mn, its maximum: if the inverse-temperature β is large enough, then Mn/ log n → 2/α β as n → ∞, in probability, where α β is given by a large deviation rate in infinite volume.We further show that, on the large deviation event that the interface connects the origin to height h, it consists of a 1D spine that behaves like a random walk, in that it decomposes into a linear (in h) number of asymptotically-stationary weakly-dependent increments that have exponential tails. As the number T of increments diverges, properties of the interface such as its surface area, volume, and the location of its tip, all obey CLTs with variances linear in T . These results generalize to every dimension d ≥ 3.