  We consider the non--equilibrium dynamics of a chain of classical rotators
coupled at its edges to an external reservoir at zero temperature. We find that
the energy is released in a strongly discontinuous fashion, with sudden jumps
alternated with long stretches during which dissipation is extremely weak. The
jumps mark the disappearance of strongly localized structures, akin to the
rotobreather solutions of the Hamiltonian model, which act as insulating
boundaries of a hot central core. As a result of this complex kinetics, the
ensemble--averaged energy follows a stretched exponential law until a residual
pseudo--stationary state is attained, where the hot core has reduced to a
single localized object.
  We give a statistical description of the relaxation pathway and connect it to
the properties of return periods of rare events in correlated time series. This
approach sheds some light into the microscopic mechanism underlying the slow
dynamics of the system.
  Finally, we show that the stretched exponential law remains unaltered in the
presence of isotopic disorder.
