  We show that the compactified extra dimension and the emergence of the island
can provide clues about quantum gravity because their combination can solve the
deepest puzzles of black hole physics. Suppose that the time dimension and the
extra dimension compactified on a circle are symmetric under \emph{double Wick
rotation}, the curvature singularity would be removed due to the end of
spacetime as a smooth bubble hidden behind the event horizon. The smooth bubble
geometries can also be interpreted as microstates leading to the
Bekenstein-Hawking entropy because the smooth bubble geometries live in the
same region of mass and charge as the black string. In addition, by applying
the quantum extremal surface prescription, we show the emergence of the island
at late times of the black string evaporation where it is located slightly
outside the event horizon. Due to the dominant contribution of the island
configuration, the entanglement entropy of the radiation grows no longer
linearly in time but it reaches a finite value that is twice the
Bekenstein-Hawking entropy at the leading order. This transition shows the
information preservation during the black string evaporation. Furthermore, we
calculate the Page time which determines the moment of the transition between
the linearly growing and constant behaviors of the entanglement entropy as well
as the scrambling time corresponding to the information recovery time of the
signal falling into the black string.
