  We propose a 1+1 dimensional CFT dual structure for quantum gravity and
matter on the extended 2+1 dimensional BTZ black hole, realized as a quotient
of the Poincare patch of AdS$_3$. The quotient spacetime includes regions
beyond the singularity, "whiskers", containing timelike and lightlike closed
curves, which at first sight seem unphysical. The spacetime includes the usual
AdS-asymptotic boundaries outside the horizons as well as boundary components
inside the whiskers. We show that local boundary correlators with some
endpoints in the whisker regions: (i) are a protected class of amplitudes,
dominated by effective field theory even when the associated Witten diagrams
appear to traverse the singularity, (ii) describe well-defined
diffeomorphism-invariant quantum gravity amplitudes in BTZ, (iii) sharply probe
some of the physics inside the horizon but outside the singularity, and (iv)
are equivalent to correlators of specific non-local CFT operators in the
standard thermofield entangled state of two CFTs. In this sense, the whisker
regions can be considered as purely auxiliary spacetimes in which these useful
non-local CFT correlators can be rendered as local boundary correlators, and
their diagnostic value more readily understood. Our results follow by first
performing a novel reanalysis of the Rindler view of standard AdS/CFT duality
on the Poincare patch of AdS, followed by exploiting the simple quotient
structure of BTZ which turns the Rindler horizon into the BTZ black hole
horizon. While most of our checks are within gravitational effective field
theory, we arrive at a fully non-perturbative CFT proposal to probe the
UV-sensitive approach to the singularity.
