Symmetry, dimensionality, and disorder play a pivotal role in critical phenomena. The atomic imaging capabilities of the scanning tunneling microscope were used to directly visualize the interaction between charge density oscillations and lattice defects in a two-dimensional charge density wave (CDW) system. Point defects act as nucleation centers of the CDW, which, as the temperature is lowered, results in the formation of pinned CDW domains that are separated by atomically abrupt charge boundaries. Incomplete freezing of substitutional disorder at low temperature indicates a novel CDW-mediated hopping of pinning centers.