The present high-resolution inelastic neutron scattering experiment on ice XVII, containing molecular hydrogen with different ortho/para ratio, allows to assign the H2 motion spectral bands to rotational and center-of-mass translational transitions of either para-or ortho-H2. Due to its structure, ice XVII confines H2 molecules to move in spiral channels of molecular size. Reported data demonstrate that H2 molecules rotate almost freely in these nanometric channels, though showing larger perturbation than in clathrate hydrates, and perform a translational motion exhibiting two low frequency excitations. The agreement between experimental spectra and corresponding molecular dynamics results clearly enables to portray a picture of the confined motions of a hydrophobic guest within a metastable ice framework, i.e. ice XVII.PACS numbers: 78.70. Nx, 63.20.Pw Ice XVII is a newly discovered form of solid water obtained from the so-called C 0 -phase of the H 2 -H 2 O binary compound, quenched at a temperature T = 77 K and ambient pressure, after letting the hydrogen molecules diffuse out of the crystal 1 . It is a pure water crystal, metastable at ambient pressure if maintained below 130 K. Its crystal structure is intrinsically porous and presents accessible channels where hydrogen molecules have been located during the production and where other molecules (belonging to hydrogen or another gas) can be absorbed again, confined in an essentially one dimensional geometry 2 . The diameter of these channels, measured from the center of the oxygen atoms, is about 6.10 A. This exotic and low-density water crystal adds to the list of solid structures of water possibly stable at negative pressure 3 .The study of the dynamics of hydrogen molecules in nano-confinement, that is intrinsically quantummechanical, is of great importance from both a practical and fundamental point of view. In hydrogen clathrate hydrates, which possess a similar chemical composition, although a different structure and stoichiometry, the hydrogen molecules confined in nearly spherical cages 4 perform an almost free rotation and a deeply non-harmonic center-of-mass (CoM) vibrational motion (rattling), both of which have been experimentally investigated by inelastic neutron scattering 5-9 and Raman scattering 10-13 . In this paper we discuss the results of a combined experimental and simulation study on the dynamics of the H 2 guests in D 2 O ice XVII and of the D 2 O host lattice.Samples for the present Inelastic Neutron Scattering (INS) experiment were produced at ISC-CNR using D 2 O and H 2 , as described in Ref.1. This isotopic composition is chosen in order to exploit the intrinsic advantage of the large incoherent neutron scattering cross-section of the proton (compared to both D and O), thus allowing for a relatively simple access to the self dynamics of molecular hydrogen. Measurements have been performed at T = 15 K on TOSCA, a high energy resolution (∆E) spectrometer at ISIS (UK) characterized by 1.5%∆E/E i 2.5%, with E i being the incoming ne...