There is a doorway there, but was it ever shown to be a turbolift?
On this page
of screencaps from Beyond the Farthest Star
, there is this
shot, which gives about the best look there is inside the second door that I recall. As one of Filmation's infamous errors, the shot evidently lacks the door elements themselves, thus revealing what's back there.
Earlier on the same page of thumbnails, you can see McCoy
exiting the main turbolift
A comparison of the backgrounds, in particular the colors and noting the presence of the silver stripe almost shoulder high, convinces me, at least, that the intent was for there to be a turbolift at the second exit, as established in the behind the scenes material that's out there.