  We offer an exact analytical equation for the void central region. We show
that the central density is solely determined by the amplitude of the initial
perturbation. Our results suggest that N-body simulations somewhat overestimate
the emptiness of voids: the majority of them should have the central
underdensity $\delta_c > -73\%$, and there should be almost no voids with
$\delta_c < -88\%$. The central region of a void is a part of an open
Friedmann's 'universe', and its evolution differs drastically from the Universe
evolution: there is a long stage when the curvature term dominates, which
prevents the formation of galaxy clusters and massive galaxies inside voids.
The density profile in the void center should be very flat. We discuss some
void models obtained by N-body simulations and offer some ways to improve them.
We also show that the dark energy makes the voids less underdense.
