Research, the rest you just fake
You must research, of course. And with the internet, it's a lot easier. You can also check the "liberry" and the used bookshops for travel guides. These are an excellent source for insight into either the actual place you're writing about, or at least places similar to it.
My mystery novels are based in modern Houston, and like many private detective books, they give the reader a tour of real streets and locales. Consider for example Robert Parker's "Spenser" and his Boston.
I use street maps and find actual routes to and fro around the city, and at times I use real restaurants and bars and such, but only if the description is positive or neutral.
For "bad" places, I make them up, cobbled together from real places I've known, selecting a detail here and a motif there, forming a new place that's realistic but still ficticious. For example, I wanted a township near Houston that's wide open -- corrupt from the top down, officials and cops and all, on the take and venal. Rather than slander a real town, I took a look at my area map. The industrialized satellite cities of Deer Park and Pasadena are contiguous. So I simply squeezed a small imaginary town between them, Mid City Texas, where anything goes.
A caution about writing about places you've never been -- don't rely on anecdote or other fiction for your sources too strongly. Likewise for "everyone knows" such and such.
If you were to write about Texas, for example, and put someone wearing fancy cowboy boots and a Stetson in downtown Houston, he'd in fact be stared at like Joe Buck in Midnight Cowboy. (with the possible exception of today -- this is opening day for the huge Houston rodeo, and they had the parade downtown). But seeing someone all tricked out in cowboy gear most times in Houston might elicit "Hey, I didn't know the circus was in town."
And even in the "outback" you'll never find someone in "rhinestone" gear unless it's a party or something. REAL cowboys (and there are plenty of them in Texas) wear boots, but they are plain bullhide and not usually shined, and they'll have on Levis or Wranglers, a workshirt, and they'll leave their hat in the pickup truck, thank you.
You won't find Houstonians saying "Yep" or "Pardner" or "Y'all" much, either, unless they're joking around.
Of course this is from a big city, 4th largest in the US. Downtown is stunning, and we have a world class opera, a major ranked symphony, and there are about 30 (not kidding) playhouses and theaters full time. We have four opera companies ("real" opera, not counting the musical theater, of which there are a half dozen at least), about a dozen ballet troupes, and many many classical venues.
So you can't impose "cowboy Texas" into Houston with impunity. Nor can you fit cookie-cutter images of Dallas or Fort Worth into Houston. The three cities are nothing alike. Likewise San Antonio, Austin, El Paso, and so on.
I'm not ranting about Texas or Houston just because I live here. All I'm saying is that you cannot rely on anecdotal evidence or "common knowledge". Instead you must obtain authentic research into the area.
If I were to attempt to write about Boston, I'd be silly to have everyone saying "Ayuh" and being fixated on the Red Sox (maybe not now, perhaps). And not everyone likes lobster.
Of course, you can create your own places, too. My WIP horror novel is set in a ficticious Texas Gulf Coast shrimping town. It doesn't exist but I've been to plenty of similar towns and so I'm using that as my structure. Some of the events occur on shrimp boats, so I got several books on shrimping and studied them, and I took photos and asked some shrimpers for permission to see their boats up close.
I can also say that what I learned first-hand wasn't too much different from my library research into shrimping. And I've found that to be true for most venues. There exist plenty of good resources for research.
Just don't assume things you can't prove by your independent research. However, that being said, it's okay to create a fictional venue, just so it's plausible.
By the way, any of you Boston folks -- I LOVE Boston. It's by far the friendliest city in the East I've visited. Had a ball at Quincy Market (sorry, "Quinzy Mahkut") and Bull & Finch (the "Cheers" bar), pigged out at Union Oyster House and Legal Seafood in Cambridge. God do I love oysters on the half-shell and lobster!