A brief overview is given on low temperature diffusive behaviour of H in Nb(OH) x , and measurement of diffusion, primarily by neutron scattering. We go in some detail into recent work on calculations of neutron structure factor as well as the diffusion coefficient of hydrogen, influenced by two-level excitations. Both the electronic and phononic contributions are covered. The importance of similar two-level excitations in insulating and metallic glasses is also pointed out.