Traditionally photons are used to study the Universe, but, at high energies, absorption of photons renders it opaque. Neutrinos, interacting only weakly, are good alternative candidates to probe the high energy Universe over cosmological distances. Pioneering experiments utilizing the neutrino as messenger have been taking data for about a decade, but so far no source of extraterrestrial high energy neutrinos could be identified. Detection requires km3 detectors, planned to be operated deep underwater or under ice. While several projects are studying the feasibility of such a detector in the Mediterranean Sea, the construction of an Antarctic array has already started.