[euix]

If you could build a sufficiently sensitive neutrino detector you could look past the ionization era of the Big Bang. What you can see in the sky is limited to that era in the cosmic history as before that period the scattering distance for photons was too short (since everything was just a free floating soap of ions) so the Cosmic microwave background (CMB) we detect is like a snapshot of the "last scattering".

But since neutrinos are only weakly coupled they fly right through without interacting most of the time. That "NMB" would presumably let us see all the way back to the big bang itself.