The visual scene that grabbed me when I saw it in the theater was the the wall behind which was the futuristic source of power for the sub. It was studded with translucent hemispheres behind which you saw the swirling colors of the process by which it was produced.
Well, that, and the tentacles of the giant squid.
Architeuthis (giant squid) really does that to subs. Eye is the size of a soccer ball - largest eyeball on the planet. Sperm whale eats em. Considered one of the largest prey/preditor matchups in the animal kingdom.