No doubt Paul is thinking about the Glass Bead Game in the puzzle he posed.

How's this:
Sistine Chapel -> curved ceiling -> planetarium -> sky -> skyscraper -> WTC -> Sept 11.
That's 5 intermediate steps.

I threw that challenge out here at home and 13 year old Alex suggested Sistine Chapel -> Catholicism -> Islam ->Terrorists -> Sept 11
That's 3 steps.

Can anyone do it in fewer moves?