The properties and nature of a highly structured photoluminescence system observed at 1.7 K in high quality bulk GaN crystals grown from a Na/Ga flux are investigated. As many as eight distinct components are resolved in the range 3.28-3.435 eV, with full widths at half maxima as narrow as 2.3 meV. In some cases, the peaks shift up or down in energy by 20 meV or more as the excitation intensity is increased. The observations are explained in terms of single or multiple polytypic quantum wells involving 3C-GaN regions embedded in the 2H-GaN matrix. We attribute the peaks to recombination of spatially separated carriers in the presence of band bending, which can be partially flattened by photogenerated carriers. The built-in fields are related to polarization charge at the 3C/2H interfaces. These PL features vary from sample to sample (or within a sample).