  Neutrinos are the best candidates to test the extreme Universe and ideas
beyond the Standard Model of particle Physics. Once produced, neutrinos do not
suffer any kind of attenuation by intervening radiation fields like the Cosmic
Microwave Background and are not affected by magnetic fields. In this sense
neutrinos are useful messengers from the far and young Universe. In the present
paper we will discuss a particular class of sources of Ultra High Energy Cosmic
Rays introduced to explain the possible excess of events with energy larger
than the Graisen-Zatsepin-Kuzmin cut-off. These sources, collectively called
top-down, share a common feature: UHE particles are produced in the decay or
annihilation of superheavy, exotic, particles. As we will review in the present
paper, the largest fraction of Ultra High Energy particles produced in the
top-down scenario are neutrinos. The study of these radiation offers us a
unique opportunity to test the exotic mechanisms of the top-down scenario.
