Fluorine mobility in monocrystalline LaF₃ is analyzed using ¹⁹F NMR spectroscopy. At lower temperatures the motion is restricted to F^- ions in the F₁ sublattice and characterized by a strongly heterogeneous behavior. Our approach which is based on line shape analysis shows that the mobility can be well described by a broad distribution of correlation times. The distribution of the correlation times and its variation with the temperature reflects the potential energy landscape in the superionic state.