  Eulerian cosmological codes are especially suited to properly describe the
low density regions. This property makes this class of codes excellent tools to
study the formation and evolution of cosmic voids. Following such ideas, we
present the results of an Eulerian adaptive mesh refinement (AMR)
hydrodynamical and N-body simulation, that contrary to the common practice, has
been designed to refine the computational grid in the underdense regions of the
simulated volume. Thus, the void regions are better described due to the
combined effect of the Eulerian character of the numerical technique and the
use of high numerical resolution from the AMR approach. To analyse the outcome
of this simulation, we have constructed a new void finder optimally suited to
find the hierarchy of voids in AMR simulations. The algorithm identifies voids
starting from the cells with least density and highest velocity divergence and
then expanding the underdense volume until reaching the void walls, defined
from the steepness of the density gradient. At redshift z=0, in a cosmological
box of comoving side length 100 Mpc/h, we identify hundreds of voids with sizes
up to 17 Mpc/h and typical density contrast of -0.8, which show a complex
morphology and an intricate hierarchy of nested structures. The analysis of
their mass density profile leads to the conclusion that a universal density
profile can be applied to voids of any size, density, morphology and redshift.
