Spin-liquids are peculiar states of matter in that they do not break any symmetries of the high temperature, magnetically disordered state, but nevertheless represent a distinct phase. The spin-liquid state is defined by the emergence of excitations which carry fractional quantum numbers and can be measured directly using neutron spectroscopy. While the existence of a spin-liquid for Heisenberg spins on the pyrochlore lattice was first speculated by Jacques Villain nearly 40 years ago, there have been no controlled experimental realizations — either classical or quantum — of this model. In real materials, the spin-liquid is more often than not preempted by small perturbations or intrinsic disorder that stabilize a broken symmetry state. In this talk, I will discuss a new material, NaCaNi₂F₇, which realizes the isotropic spin liquid of Villain but with the additional complication of random Na⁺ – Ca²⁺ charge disorder in the crystal structure. We use neutron scattering and calorimetric measurements to uncover the magnetic correlations in this material and fully determine the magnetic Hamiltonian. The ionic disorder creates a rugged energy landscape that acts to freeze a small fraction of the magnetic degrees of freedom in time. However, the energy scale set by this disorder is small, and the Heisenberg interactions prevail. In fact, only 40% of the available moment is frozen, and the magnetism in NaCaNi₂F₇ is dominated by a persistently fluctuating component. These measurements provide the first experimental confirmation of Villain’s prediction and a new insight into the interplay between disorder and magnetic exchange interactions in highly frustrated magnets.