Comment by idbehold
I'm sure it's not practical, but I always thought it would be interesting if instead of living "inside" a black hole, the visible universe was simply being consumed by a black hole so large it just encompassed everything outside the visible part. So no nesting, the universe just eventually gets consumed entirely by one black hole.
Unsure if the math actually checks out on this, but I was told that if you add up the observable mass/energy in our universe with the same average density we see now, you get a black hole with a Swarzchild radius around the size as the observable universe.
One could then quite reasonably argue that our universe is indeed inside or is itself a black hole.