^^ Oops...mea culpa. It's there but apparently I didn't erase the corridor floor lines to better simulate the opening. It's between Kirk's bedroom and Recreation Room 4, i.e. the corridor where Spock suddenly popped up to join Kirk and McCoy (perfect Vulcan timing
At first, I couldn't make up my mind whether there was a bathroom at the end of the corridor or a stairway down to Deck 6.
I went for the stairway solution because it's going to be the same stair area Spock used in "Wink of an Eye" on Deck 6 to join with Kirk and the security crewmen to examine Environmental Engineering.
The inevitable problem with horizontal turboshafts is that these separate the sections on Deck 6 from one another, thus the crew either has to "climb" over these shafts or "crawl" beneath them.