Cosmic rays with energies up to a few PeV (=1e15 eV), the "knee“ in the CR spectrum, are believed to be of Galactic origin.The current paradigm is that Galactic cosmic rays up to PeV energies are accelerated in the shells of supernova remnants (SNRs). SNRs would be the Galactic PeVatrons. This hypothesis is, however, not supported by observational evidence. Multi TeV gamma-rays, produced by cosmic rays (CRs) interacting in the interstellar medium, are the best tracers of the parental CR population close to the knee. Recently, the TeV observatory, H.E.S.S., has discovered a handful of potential PeVatron candidates, which have no clear counterparts such as SNRs, at low energies. I will report on these recent discoveries and discuss prospects for current and future gamma-ray observatories.