In "The Making of Star Trek," Stephen Whitfield refers to the TOS Enterprise having a large recreation area featuring "outdoor" simulation. On pages 187 - 188 he writes, "Although this recreation area has never been shown in any past Star Trek episodes, this set has now been built and will be seen in the third season."
He goes on to include Gene Roddenberry's description of this rec area which Roddenberry explains, "Therefore, we intend to build a simulated "outdoor" recreation area which gives a realistic feeling of sky, breezes, plants, fountains, and so forth."
The only area on the TOS ship that bears any similarity to an "outdoor" setting is the botany lab which has plants. Indeed, the botany lab is shown in "And The Children Shall Lead"
and "Is There in Truth No Beauty,"
both third season episodes, but it is also previously shown in "The Man Trap,"
a first season episode.
Would the botany lab set also be considered this "outdoor" setting Roddenberry described? If not, it would seem rather odd that crew members would be allowed to bring their food in at any time and socialize ("The Man Trap"),
or kids would be allowed to enter and run around ("And The Children Shall Lead")
in a scientific lab where botanical research is being conducted.