  The far-IR is a unique wavelength range for Astrophysical studies, however,
it can only be fully sampled from space platforms. The fundamental rotational
transitions of light molecules, the high-J transitions of polyatomic species,
the bending modes of non-polar molecules, several atomic fine structure lines
and many frequencies blocked by the earth atmosphere can only be observed
between 50 and 200 um (6.0 and 1.5 THz). In this contribution we present the
far-IR spectrum of Sgr B2 at a resolution of ~35 km s^{-1}, the ``Rosetta
stone'' of ISO's far-IR spectra. We also discuss the perspectives of the far-IR
Astronomy in the context of the future telescopes under development.
