How dull. Glad they didn't go that route.
Did Gene ever try to explain how they'd actually pull that off? I doubt living in an underground cavern would be a pleasant experience.
The claustrophobia would be off the charts...
Nothing specific that I can recall in terms of the underground cities. @Maurice might recall more. But lots of TGT script and early TMP drafts show humans frolicking in parks. There's an opening sequence of Kirk swimming in the Bay. So humans weren't confined to those dwellings. But seemed one with nature.