  Horizons of black holes or cosmologies are peculiar loci of spacetime where
interesting physical effects takes place, some of which are probed by recent
(EHT and LIGO) and future experiments (ET and LISA). We discuss that there are
boundary degrees of freedom residing at the horizon. We describe their
symmetries and their interactions with gravitational waves. This fits into a
larger picture of boundary plus bulk degrees of freedom and their interactions
in gauge theories. Existence and dynamics of the near horizon degrees of
freedom could be crucial to address fundamental questions and apparent
paradoxes in black holes physics.
