  We study axion-photon couplings in compactifications of type IIB string
theory. We find that these couplings are systematically suppressed compared to
the inverse axion periodicity, as a result of two effects. First, couplings to
the QED theta angle are suppressed for axion mass eigenstates that are light
compared to the mass scale set by stringy instantons on the cycle supporting
QED. Second, in compactifications with many axions the intersection matrix is
sparse, making kinetic mixing weak. We study the resulting phenomenology in an
ensemble of $200{,}000$ toy models constructed from the Kreuzer-Skarke database
up to the maximum Hodge number $h^{1,1}=491$. We examine freeze-in production
and decay of thermal axions, birefringence of the cosmic microwave background,
X-ray spectrum oscillations, and constraints on the QCD axion from supernovae.
We conclude that compactifications in this corner of the landscape involve many
invisible axions, as well as a handful that may be detectable via photon
couplings.
