  In the next 30 years, a new generation of space and ground-based telescopes
will permit to obtain multi-frequency observations of faint sources and, for
the first time in human history, to achieve a deep, almost synoptical
monitoring of the whole sky. Gravitational wave observatories will detect a
Universe of unseen black holes in the merging process over a broad spectrum of
mass. Computing facilities will permit new high-resolution simulations with a
deeper physical analysis of the main phenomena occurring at different scales.
  Given these development lines, we first sketch a panorama of the main
instrumental developments expected in the next thirty years, dealing not only
with electromagnetic radiation, but also from a multi-messenger perspective
that includes gravitational waves, neutrinos, and cosmic rays. We then present
how the new instrumentation will make it possible to foster advances in our
present understanding of galaxies and quasars. We focus on selected scientific
themes that are hotly debated today, in some cases advancing conjectures on the
solution of major problems that may become solved in the next 30 years.
