We report quasi-elastic neutron scattering (QENS) and optical spectroscopic measurements of the proton motion in the hydrogen bond of benzoic acid crystals, a system in which proton transfer occurs in a near-symmetric double-well potential and both coherent and incoherent proton tunneling have been measured. Inter-well relaxation is characterized by a correlation time that determines the width of the QENS line. Our new measurements cover the transition from the classical to the quantum regime. The optical spectroscopic data, using new dopant molecules, extend measurements of the proton dynamics to very low temperatures, where coherent tunneling is observed. Theoretical methods, based on a perturbative instanton approach, have been developed to describe tunneling in multidimensional potential energy surfaces and are used to model our observations.