Compactifications of the heterotic string with eight supercharges provide
a rich corner of the string landscape, in which fluxes can be analyzed
directly from the worldsheet perspective. The underlying geometry of such
4-dimensional compactifications is a principal torus bundle over a K3
surface, and is generically non-Kähler. In this talk, I will focus on the
interrelation between topology and Narain T-duality of heterotic flux
vacua. Specifically, I will present evidence that T-duality in the torus
fiber can relate all such backgrounds to flux-free compactifications on a
K3$\times T^2$ product geometry. In addition, I will emphasize the role of
global and flat structures in the resulting web of equivalent geometries.