To reduce the amount of friction caused by adding this new feature, I would maintain most all of the established design, layout and interaction patterns that users are accustomed to in the existing Instagram product. I would start by adding a tab to the Search / Discover page allowing users to follow the same paradigm but with a focus on locations.
The Locations Search / Discover initial screen would look very similar to the Posts Search / Discover screen. It would have a slideshow of curated content below the tabs, a grouping of trending locations, and at the bottom, an interactive map.
On a single tap, the map slides up to take up all of the available screen. Dots on the map represent locations with a cluster of posts. Tapping on one of the dots allows the user to get a quick peek at the posts in that location displaying 8 at a time.
Sliding up on the quick peek, or clicking on the 'More' link will reveal the full list of results for that location
Furthermore, a user will have the ability to limit the posts they view in a given location by a date range. Users will also have the ability to look at several locations and dates in the same result set.
By tapping the location above the results a user is presented with the current date and time. From this screen a user can edit their current selections or add another date and location to their results.
This feature exploration is purely for fun and not associated with Instagram in any way.
If you'd like to see how it was built, you can check out my Sketch source file here.