  We examine indirect detection of dark matter that annihilates into dark
glueballs, which in turn decay into the Standard Model via a range of portals.
This arises if the dark matter candidate couples to a confining gauge force
without light flavours, representative of many possible complex dark sectors.
Such Hidden Valley scenarios are being increasingly considered due to
non-detection of minimal models as well as theoretical motivations such as the
Twin Higgs solution to the little hierarchy problem. Study of dark glueballs in
indirect detection has previously been hampered by the difficulty of modeling
their production in dark showers. We use the recent GlueShower code to produce
the first constraints on dark matter annihilating via dark glueballs into the
Standard Model across photon, antiproton, and positron channels. We also fit
the Galactic Centre Excess and use this observation, combined with other
astrophysical constraints, to show how multi-channel observations can constrain
UV and IR details of the theory, namely the exact decay portal and
hadronization behaviour respectively. This provides unique complementary
discovery and diagnostic potential to Hidden Valley searches at colliders. It
is interesting to note that thermal WIMPs annihilating to
$\mathcal{O}(10~\mathrm{GeV})$ dark glueballs and then the Standard Model via
the Twin-Higgs-like decay portal can account for the Galactic Centre Excess
while respecting other constraints.
