  We show that in a wide class of string derived models of particle physics,
heavy string modes with masses around the GUT scale can serve as a viable dark
matter candidate. These heavy string modes wind around specific cycles in the
extra-dimensional space, closely related to the fundamental group $\pi_1$. As a
consequence of a non-trivial $\pi_1$, there is an exact discrete symmetry that
stabilizes such winding strings. The dark matter candidate couples to the
Standard Model via gravity and via the exchange of heavy string states. We find
that, for reasonable values of the string coupling, our dark matter candidate
can be produced in sizable amounts via freeze-in. Our scheme applies to many
string constructions, including Calabi-Yau compactifications, and can be tested
against constraints from the CMB.

High Energy Physics - Phenomenology;High Energy Physics - Theory