If you're writing fanfiction, of course, many of these details are already spelled out for you, but straying outside of canon might also involve world-building details.
If you're going strictly fictional, particularly in sci-fi, fantasy, dystopian or something else, there is a LOT more work involved in making your location come alive (and helping make sure the continuity police aren't on your case about discrepancies ;) )
Here are some sites that offer helpful tips and guidelines to think about when shaping the world in which your characters live.
https://www.ambient-mixer.com/ (for invoking sounds you might hear in your setting. Warning...it is very easy to get lost in here ;) lol)