  Recently, at least 50 million of novel examples of compact $G_2$ holonomy
manifolds have been constructed as twisted connected sums of asymptotically
cylindrical Calabi-Yau threefolds. The purpose of this paper is to study mirror
symmetry for compactifications of Type II superstrings in this context. We
focus on $G_2$ manifolds obtained from building blocks constructed from dual
pairs of tops, which are the closest to toric CY hypersurfaces, and formulate
the analogue of the Batyrev mirror map for this class of $G_2$ holonomy
manifolds, thus obtaining several millions of novel dual superstring
backgrounds. In particular, this leads us to conjecture a plethora of novel
exact dualities among the corresponding 2d N=1 sigma models.
