Decades ago, I took 2 semesters of Gravitation and Cosmology in grad school (ala: Misner, Thorne and Wheeler), and 4 semesters of Quantum (Thru QED). However, I've never had the opportunity to apply any of this to the real-world. I'm still at work in Applied Physics, using Classical concepts. Nevertheless, I maintain a pedestrian interest in these more Esoteric concepts.