The spectrum above 100 GHz has the potential to enable accurate 3D wireless localization due to the large swath of available spectrum. Yet, existing wide-band localization systems utilize the time of arrival measurements requiring strict time synchronization. In this paper, we present 123-LOC, a novel non-coherent system for one-shot dual-polarized 3D localization above 100 GHz. Our key idea is to create unique asymmetric THz fingerprints in 3D so that a wireless node can jointly infer its angular position and distance by taking hints from the measured power-spectrum profile. We introduce a dual-polarized dual-slit waveguide structure that emits out signals into free-space with a key feature that the beam pattern depends on the frequency of the signal and the geometry of the slit. To distinguish the emissions from the two slits, we use polarization diversity and manipulate the aperture geometry of the two slits so that they transmit slightly different angular-spectral signatures. Our over-The-Air experiments demonstrate that 123-LOC achieves an average angle estimation error of 1° together with millimeter-scale ranging resolution, solely through non-coherent power measurements.