  We use molecular dynamics computer simulations and nuclear magnetic resonance
experiments to investigate the dynamics of water at interfaces of molecular
roughness and low mobility. We find that, when approaching such interfaces, the
structural relaxation of water, i.e., the $\alpha$ process, slows down even
when specific attractive interactions are absent. This prominent effect is
accompanied by a smooth transition from Vogel to Arrhenius temperature
dependence and by a growing importance of jump events. Consistently, at protein
surfaces, deviations from Arrhenius behavior are weak when free water does not
exist. Furthermore, in nanoporous silica, a dynamic crossover of liquid water
occurs when a fraction of solid water forms near 225 K and, hence, the liquid
dynamics changes from bulk-like to interface-dominated. At sufficiently low
temperatures, water exhibits a quasi-universal $\beta$ process, which is
characterized by an activation energy of $E_a\!=\!0.5$ eV and involves
anisotropic reorientation about large angles. As a consequence of its large
amplitude, the faster $\beta$ process destroys essentially all orientational
correlation, rendering observation of a possible slower $\alpha$ process
difficult in standard experiments. Nevertheless, we find indications for the
existence of structural relaxation down to a glass transition of interfacial
water near 185 K. Hydrated proteins show a highly restricted backbone motion
with an amplitude, which decreases upon cooling and vanishes at comparable
temperatures, providing evidence for a high relevance of water rearrangements
in the hydration shell for secondary protein relaxations.
