  Domain walls (DWs) are topological defects originating from phase transitions
in the early universe. In the presence of an energy imbalance between distinct
vacua, enclosed DW cavities shrink until the entire network disappears. By
studying the dynamics of thin-shell bubbles in General Relativity, we
demonstrate that closed DWs with sizes exceeding the cosmic horizon tend to
annihilate later than the average. This delayed annihilation allows for the
formation of large overdensities, which, upon entering the Hubble horizon,
eventually collapse to form Primordial Black Holes (PBHs). We rely on 3D
percolation theory to calculate the number density of these late-annihilating
DWs, enabling us to infer the abundance of PBHs. A key insight from our study
is that DW networks with the potential to emit observable Gravitational Waves
are also likely to yield detectable PBHs. Additionally, we study the production
of wormholes connected to baby-universes and conclude on the possibility to
generate a multiverse.
