  Motivated by a recent construction of non-supersymmetric $\text{AdS}_3$, we
revisit the $O(16)\times O(16)$ heterotic string compactified on a torus. The
string one-loop potential energy has interesting dependence on the classical
moduli; extrema of this potential include loci where the gauge symmetry is
maximally enhanced. Focusing on the case of a circle, we use lattice embeddings
to find the maximal enhancement points together with their spectra of massless
and tachyonic modes. We find an extended Dynkin diagram that encodes the global
structure of the moduli space, as well as all symmetry enhancements and the
loci where they occur. We find $107$ points of maximal enhancement with $8$
that are free of tachyons. The tachyon-free points each have positive
cosmological constant. We determine the profile of the potential energy near
each of these points and find that one is a maximum while three are saddle
points. The remaining four live at the boundary of a tachyonic region in field
space. In this way, we show that every point of maximal symmetry enhancement is
unstable. We further find that the curvature of this stringy potential
satisfies the de Sitter swampland conjecture. Finally, we discuss the
implications for constructions of $\text{AdS}_3$.
