6. Ketha Province
When the Away Team heads to the Klingon world of Qo'noS, they travel to a specific region called the Ketha Province, which no doubt warmed the cockles of many Trekkies sitting in the audience, given that this is where General Martok - who fans will remember from Deep Space Nine - comes from. Though Harrison choosing to beam in here doesn't make any specific causal link between the two, it's a nice nod to those who are fans of not just TOS, but the wider-reaching series attached to it like DS9 and Voyager.