  Nature produces cosmic ray particles, probably protons, with energies well
above $10^{20}$ eV -- how are they produced? Where do they come from? Gamma
rays with energies above $10^{13}$ eV are produced in jets of active galaxies
-- are these produced by energetic electrons or protons? What is the correct
model of Gamma Ray Bursts? These are just some of the fundamental questions in
high energy astrophysics to be answered by observations made with large area
neutrino telescopes.
