  Using the relativistic Fermat's principle, we establish a bridge between
stationary-complete manifolds which satisfy the observer-manifold condition and
pre-Randers metrics, namely, Randers metrics without any restriction on the
one-form. As a consequence, we give a description of the causal ladder of such
spacetimes in terms of the elements associated with the pre-Randers metric: its
geodesics and the associated distance. We obtain, as applications of this
interplay, the description of conformal maps of Killing submersions, and
existence and multiplicity results for geodesics of pre-Randers metrics and
magnetic geodesics.
