Forget all the screenshots and "guides" here, just watch the video and you get it within 1 minute. All the picture guides here are way too complicated and sometimes even wrong.
Other guy's pics confused me since he has terrible map settings, so here are some better pictures. PSA: set map viewing angle to 90 degrees and don't turn on rotate minimap.
I auto-pathed to Yianaros's Field, but stopped before going through the tunnel
There's a big cliff that juts out just before you reach the tunnel. I slid down that and followed some of the other screenshots here to get to the right spot.
The exploration point is in a bigger tunnel
My horse is sitting where I stopped just before the tunnel to Yianaros, and where I'm standing at is where the exploration point is.