  We propose a new $AdS_3/CFT_2$ duality, in which the bulk string theory has a
target spacetime $AdS_3$ times a squashed three-sphere $S^3_\flat$, and the
dual $CFT_2$ is a symmetric product of sigma models on $R_\phi\times
S^3_\flat$, deformed by a $\phi$-dependent $Z_2$ twist operator. The duality
maps the asymptotic region of $AdS_3$ to the region $\phi\to\infty$, where the
twist interaction in the $CFT_2$ turns off. The $AdS_3$ backgrounds in question
have $R_{AdS}<\ell_s$, and so lie on the string side of the string/black hole
correspondence transition. As a consequence, the high energy density of states
consists of a string gas in $AdS_3$ rather than an ensemble of BTZ black holes.
This property allows us to derive the dual $CFT_2$ by a systematic analysis of
the worldsheet string theory on $AdS_3$.
