  The objective of neutrino astronomy, born with the identification of
thermonuclear fusion in the sun and the particle processes controlling the fate
of a nearby supernova, is to build instruments which reach throughout and far
beyond our Galaxy and make measurements relevant to cosmology, astrophysics,
cosmic-ray and particle physics. These telescopes will push astronomy to
wavelengths smaller than $10^{-14}$~cm by mapping the sky in high-energy
neutrinos instead of high-energy photons to which the Universe is partially
opaque. While a variety of collaborations are pioneering complementary methods
by building neutrino detectors with effective area in excess of 0.01~km$^2$, we
show here that the science dictates 1~km$^2$, or a 1~km$^3$ instrumented
volume, as the natural scale of a high-energy neutrino telescope. The
construction of a high-energy neutrino telescope therefore requires a huge
volume of very transparent, deeply buried material such as ocean water or ice,
which acts as the medium for detecting the particles. We will speculate on its
architecture. The field is immersed in technology in the domain of particle
physics to which many of its research goals are intellectually connected. With
several thousand optical modules the scope of constructing a kilometer-scale
instrument is similar to that of experiments presently being commissioned such
as the SNO neutrino observatory in Canada and the Superkamiokande experiment in
Japan.
