This thesis is devoted to the study of quantum vacuum effects in the presence of strong gravitational fields. We shall see how the quantum vacuum interacts with black hole geometries and how it can play an important role in the interpretation of the gravitational entropy. In this respect particular attention will be given to the peculiar role of the extremal black hole solutions. From this branch of our research we shall try to collect some important hints about the relation between quantum gravity theories and the semiclassical results. After these investigations we shall move our attention toward possible experimental tests of particle creation from the quantum vacuum which is an indirect confirmation of the Hawking effect. This aim will lead us to study acoustic geometries and their way of "simulating" General Relativity structures, such as horizons and black holes. We shall study the stability of these structures and the problems related to setting up experimental detection of phonon Hawking flux from acoustic horizons.
