OSINT
Open Source Intelligence - Gathering information accessible to the general public for a purpose
Usually involves a lot of looking around. All of the information is available, you just need to know where to look!
OSINT is pretty much cyberstalking. Always make sure you have complete approval before conducting an OSINT search on someone/something. As with most of CTFs, don't touch anything you aren't allowed to. ESPECIALLY WITH OSINT, DO NOT ATTEMPT ANYTHING OUTSIDE OF ETHICAL/LEGAL BOUNDARIES!! Also, make sure to not be invasive/intrusive during OSINT investigations (respect people's privacies)
aka Geoguessr if it was useful
In CTFs, unlike Geoguessr, we're usually looking for a way more specific area. A typical CTF geo-osint challenge will give an image with/without context that would allow someone to narrow an area down to a very precise location. For instance, we might get an image like this:
If you look at the right edge of the image, we see The Cube in the picture, as well as the orientation of the walkway. Going onto Google Maps, we can find a spot that matches all of the aspects of the photo. This allows us to determine exactly where this photo was taken, (42.2755, -83.7425)
Although most of this is just manually looking through google maps and street view off whatever clues you are given, there are multiple tools and tricks to look for in these challenges. Also, geoguessr knowledge (aka knowing geographical details between countries/continents) is pretty helpful in getting the general area first.
Usually, the faces of the people in a photo will be blurred out but you can still look at their clothing, style and general characteristics to determine more about the location
If you have anything of curiosity, then there is probably a tool to help you with it