  Ionization cones and relativistic jets give us one of the most large-scale
example of active galactic nuclei (AGN) influence on the surrounding gas
environment in galaxies and beyond. The study of ionization cones makes it
possible not only to test the predictions of the unified model of galactic
activity, but also to probe galaxy gas environment and trace how the luminosity
of the nucleus changes over time (a light echo). In the external galactic or
even extragalactic gas ionization cones create Extended Emission-Line Regions
(EELRs) which can span distances from several to hundreds kpc away a host
galaxy. We review the recent results of studying the gas kinematics and its
ionization properties in EELRs with a special attention to search of fading AGN
radiation on the time scale $\mbox{few}\times(10^4-10^5)$ yr. The role of
modern narrow-band and integral-field surveys in these researches is also
considered.
