  In this work we consider black holes surrounded by anisotropic fluids in four
dimensions. We first study the causal structure of these solutions showing some
similarities and differences with Reissner-Nordstr\"om-de Sitter black holes.
In addition, we consider scalar perturbations on this background geometry and
compute the corresponding quasinormal modes. Moreover, we discuss the late-time
behavior of the perturbations finding an interesting new feature, i.e., the
presence of a subdominant power-law tail term. Likewise, we compute the
Bekenstein entropy bound and the first semiclassical correction to the black
hole entropy using the brick wall method, showing their universality. Finally,
we also discuss the thermodynamical stability of the model.
