A key to realize better functional properties in electroceramics resides on the control of its microstructure over several length scales. Especially for the development of new lead-free antiferroelectrics the microstructural characteristics are essential to avoid the coexistence of the antiferroelectric phase with the ferroelectric polymorph at room temperature, which restrains the energy efficiency. The current mechanistic understanding of the defect-tuned energy storage functionalities has been limited due to complex lattice dynamics and hierarchical morphology in antiferroelectrics. There extrinsic and intrinsic bulk behavior is hardly understood due to the lack of experimental techniques able to probe features which are embedded inside the bulk. To overcome such an experimental limitation, we investigate the structure-property relationship of antiferroelectric oxides with Dark-field X-ray microscopy. This new non-destructive synchrotron technique enables a high-resolution visualization of domains, grain distribution, and strains within the bulk. In this work we focus on the interplay between crystal structure, domain, and grain morphologies in NaNbO3 polycrystals. The observed morphological domain evolution from the high temperature paraelectric phase towards the antiferroelectric rhombohedral phase at room temperature is discussed in terms of phase-dependent strain and orientation distributions during the phase transitions in this polymorphic material.