Strong electron correlations in bulk materials lead to exotic states of matter that often display high degree of quantum entanglement. A prototypical example are heavy-fermion materials where electronic correlations at the brink of delocalization result in unconventional superconductivity, strange-metal behavior, spin-triplet superconductivity, or quantum critical regimes. A major hurdle in this area is that heavy fermions are mostly studied phenomenologically whereas microscopic understanding remains often elusive. The Kondo-lattice model, which captures the underlying correlations, is notoriously difficult to solve for real materials and was—until recently—never solved quantitatively. I will present an example, where we succeeded—for the first time—to model a real bulk heavy-fermion material from first principles. The results were validated with high-resolution neutron spectroscopy. I will further introduce new spectroscopy techniques, which provide direct and unprecedented insights into the entanglement structure of electrons in bulk materials. In conjunction, these approaches may represent exciting new pathways to unravel long-standing mysteries of heavy fermions, most notably unconventional pairing mechanisms.