Instagram assigns its registered locations with a Location ID, which is a string of numbers. Some plugins and feeds can use that location ID to act as a filter to display photos from that place, much the same way you can filter using hashtags.
But how to find that number isn't self-evident. So here's the quick way to find Instagram's location ID for any given place.
1. Log In
Log into the Instagram website (instagram.com) using a web browser.
2. Search for Location
In the search bar, type the name of the place. As you type, you'll see a list of results update in real time. This will be a combination of places, hashtags, and usernames. What you want to look for are the locations, and they're identified with the map marker icon, like this:
3. Open Location Page
Click on the location result. You'll go to the location results page, which will have a map at the top and a grid of photos from that location below.
4. Copy Location ID
Look in the browser's URL bar. You'll have something along these lines. What you want is the string of digits in the second-last section, like this:
5. Copy & Paste Location ID
Copy those numbers and paste them into whatever plugin or feed you're using.
Doing it Programmatically using Instagram's API
Obviously, this isn't a practical way to do it programmatically if you're developing an app or script. For that you'll want to consult Instagram's Locations Endpoints section of the API documentation.