i will explain recent results on modular, geometrically meaningful compactifications of moduli spaces of k3 surfaces, most of which are joint with philip engel. a key notion is that of a recognizable divisor: a canonical choice of a divisor in a multiple of the polarization that can be canonically extended to any kulikov degeneration. for a moduli of lattice-polarized k3s with a recognizable divisor we construct a canonical stable slc pair (ksba) compactification and prove that it is semi toroidal. we prove that the rational curve divisor is recognizable, and give many other examples.