Think of where this is located---Deck 3. There are cabins (with windows) on the outer "hull" (check the deck plans). The "heavy glass" are mirrors---look carefully, one can see the reflected image. It's a great illusion.
Do I dare pop the bubble and reveal it's not the hull? It's another art installation---on the other side is the hallway to the Deck 3 cabins.
Oops. I gues I did.