The recent observations of photons with energies of a few 1014 eV from decaying neutral pions, both from a direction coincident with a giant molecular cloud (HAWC J1825-134, Albert et al. 2021) and from the Galactic plane (Amenomori et al. 2021), provide evidence for an acceleration of cosmic rays to energies of several 1015 eV, and above, in the Galaxy. A dozen sources emitting photons with energies up to 1015 eV have even been reported (Cao et al. 2021a), and in at least one of them (LHAASO J2108+ 515, also in directional coincidence with a giant molecular cloud), these photons might have a hadronic origin (Cao et al. 2021b). Observations of these photons are key in probing the mechanisms of particle acceleration, completing the multi-messenger approach aimed at understanding the nonthermal processes producing cosmic rays. The detection of even higher-energy photons would be of considerable interest in discovering extreme accelerators in the Galaxy. Also, should one detect photons of such energies clustered preferentially in the direction of the Galactic center, then this could highlight the presence of super-heavy dark matter (SHDM) produced in the early universe and decaying today (see, eg, Benson et al. 1999; Berezinsky &