The energy spectrum of cosmic rays beyond the turn-down around $$\varvec{10^{17}}$$ eV as measured with the surface detector of the Pierre Auger Observatory

We present a measurement of the cosmic-ray spectrum above 100\,PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750~m. An inflection of the spectrum is observed, confirming the presence of the so-called \emph{second-knee} feature. The spectrum is then combined with that of the 1500\,m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks...