Despite being proven to be a good lithium-ion conductor 30 years ago, the crystal structure of the ramsdellite-like Li2Ti3O7 has remained uncertain, with two potential models for locating the lithium ions in the structure. Although the model presently accepted states that both lithium and titanium occupy the octahedral sites in the framework, evidence against this model are provided by Li-6 and Li-7 MAS NMR spectroscopy. Thus, about 14% of these octahedral positions are empty since no lithium in octahedral coordination is present in the material. When Li2Ti3O7-ramsdellite is treated with nitric acid a complete exchange of lithium by protons is produced to yield H2Ti3O7. The crystal structure of this proton-exchanged ramsdellite has been re-examined combining X-ray diffraction (XRD), neutron powder diffraction (NPD), and spectroscopic (H-1 and Li-7 MAS NMR) techniques. Two kinds of protons are present in this material with different acidity because of the local environments of oxygen atoms to which protons are bonded, namely, low acidic protons strongly bonded to highly charged oxygen atoms (coordinated to two Ti4+ and a vacancy); and protons linked to low charged oxygen atoms (bonded to three Ti4+ ions) which will display a more acidic behavior. H2Ti3O7 absorbs water; proton mobility is enhanced by the presence of absorbed water, giving rise to a large improvement of its electrical conductivity in wet atmospheres. Thus, it seems that water molecules enter the tunnels in the structure providing a vehicle mechanism for proton diffusion.