  Molecular rotation, vibration, internal rotation, isomerization, tunneling,
intermolecular dynamics of weakly and strongly interacting systems,
intra-to-inter-molecular energy transfer, hindered rotation and hindered
translation over surfaces are important types of molecular motions. Their
fundamentally correct and detailed description can be obtained by solving the
nuclear Schr\"odinger equation on a potential energy surface. Many of the
chemically interesting processes involve quantum nuclear motions which are
`delocalized' over multiple potential energy wells. These `large-amplitude'
motions in addition to the high dimensionality of the vibrational problem
represent challenges to the current (ro)vibrational methodology. A review of
the quantum nuclear motion methodology is provided, current bottlenecks of
solving the nuclear Schr\"odinger equation are identified, and solution
strategies are reviewed. Technical details, computational results, and analysis
of these results in terms of limiting models and spectroscopically relevant
concepts are highlighted for selected numerical examples.
