Ten years after their discovery, fundamental questions on the extragalactic fast radio bursts (FRBs) remain open: (1) what are their progenitors? (2) what is the nature of the medium through which they propagate? The extreme diversity of the FRB sample in the estimated burst energies, temporal profiles, and polarization properties makes it difficult to identify individual populations. Similarly, the diversity of propagation signatures (including dispersion, scattering, and Faraday rotation in intervening inhomogeneous, magnetized plasma) prevents us from identifying the typical FRB distance scale and progenitor environment. Accurate localization of FRBs, which is technically difficult when they are first detected, is therefore crucial for further progress. I shall describe efforts at Caltech to construct a dedicated FRB localization instrument. The successful deployment of a ten-antenna prototype has motivated us to begin construction of a 110-antenna array (the Deep Synoptic Array; DSA) that will localize > 100 FRBs/year to <3 arcseconds. I will outline the expected outcomes of the DSA, focusing on its potential for the study of physical conditions in the circum-/intergalactic medium.