In the world I'm building, there is a race of people whose main shtick is that they can detect the magnetic fields of their planet and use them to navigate. In one of their cultures, the people are nomadic and use the same "roads" to travel to different historic or religious sites in their culture. What's even more interesting is their sense of these lines, which is widely perceived as being innate knowledge. Members of this culture may not know where these paths lead, but their existence is widely known and understood to them, even if they've never followed them far or at all.
However, what these ley lines really are has been difficult to pin down. I am essentially looking for a phenomenon that can explain the following traits:
Ley lines can be felt, but cannot be seen with the naked eye
They will continue to be present regardless of terrain or manmade constructs, and can be tracked going “through” things as well
Ley lines can be of varying length
They do not have to intersect, although this would be preferred if possible
The shape of the line is of little consequence, but straighter lines would be preferred if possible
Their existence is part of some natural force that does not need to be taught
Ley lines are not the magnetic field of the planet, although they may be related to magnetic forces
Ley lines are not a phenomenon caused by any extinct cultures or anything like that; this is a natural force of the world
They are also not a creation of the gods or magic
In essence, I am looking for a natural phenomenon or something that could be a widespread phenomenon on some other world to use in this setting that meets most if not all the criteria above.