  The riddle of the origin of Cosmic Rays is open since one century. Recently
we got the experimental proof of hadronic acceleration in Supernovae Remnants,
however new questions rised and no final answer has been provided so far. Gamma
ray observations above 100 MeV reveal the sites of cosmic ray acceleration to
energies where they are unaffected by solar modulation. In the last years the
knowledge in this field of research widely increased, however almost 50% of the
TeV (> 10^12 eV) Galactic sources are still unidentified, at GeV (> 10^9 eV)
energies, 67% of EGRET sources were unidentified and also with the newer
generation of gamma-ray satellites we have the same result: in fact, at low
Galactic latitudes (b<10 deg), 62% of the Fermi LAT detected sources have no
formal counterpart. Hence understanding the high energy unidentified sources
will be a crucial brick in solving the whole riddle of Cosmic Rays origin.
Several examples will be shown, underlining the importance of the so-called
"dark sources". Both theoretical aspects (with particular emphasis to the
so-called Ancient Pulsar Wind Nebulae scenario) and their observational proofs
will be discussed.
