  We study Lorentzian eternal black holes in the Chern-Simons sector of AdS$_3$
higher spin gravity. We probe such black holes using bulk Wilson lines and
motivate new regularity conditions that must be obeyed by the bulk connections
in order for the geometry to be consistent with an interpretation as a
thermofield state in the dual CFT$_2$. We demonstrate that any higher spin
black hole may be placed in a gauge that satisfies these conditions: this is
the Chern-Simons analogue of the construction of Kruskal coordinates that
permit passage through the black hole horizon. We also argue that the Wilson
line provides a higher-spin notion of causality in higher spin gravity that can
be used to associate a Penrose diagram with the black hole. We present some
applications of the formalism, including a study of the time-dependent
entanglement entropy arising from the higher spin black hole interior and
evidence for an emergent AdS$_2$ region in the extremal limit.
