Andrew Probert gave the rear of the refit Enterprise superstructure four large windows. It was only glimpsed from the inside once, when Spock’s shuttle approaches the ship in The Motion Picture. But this is where the officers’ lounge scene between Kirk, Spock and McCoy was meant to take place.
Lora (then Shane) Johnson writes in Mr Scott’s Guide to the Enterprise that the reason the scene was filmed in a smaller room is because The Motion Picture had already run over budget.
“The briefing room scene was rewritten for an ‘officers’ lounge’,” Johnson told Greg Tyler of Trekplace, “and a set was created somewhat hastily using existing ‘rec deck’ components.”
Probert rationalized the scene by suggesting that the space could be a secluded area within a larger officers’ lounge. That is also the approach Johnson took in Mr Scott’s Guide to the Enterprise.
The 2001 Director’s Edition of The Motion Picture replaced the black screen behind Spock with a view of the starboard nacelle, suggesting the room might be in the back of the saucer section. Although that could also, of course, simply be a projection.
In canon, the layout of the rest of Decks 2 and 3 is unknown. Mr Scott’s Guide suggests Deck 2 is home to security facilities and Deck 3 has a large officers’ mess and lounge surrounding a kitchen, which is seen in Star Trek VI: The Undiscovered Country.
The forward end of the superstructure features a series of details on the outer hull which have not been officially identified. Franz Joseph’s deck plans for the original Enterprise placed science labs in the front section of Deck 2, suggesting these may be sensor pallets.