In “the courtyard” I am able to path through almost the entire map by “attempting” to cross the broken bridge by the entrance. I was even able to do this before the map was revealed so my character just followed the path even though I the player had no knowledge of the route.
Here is a link to a screenshot where I have painted the path my character took with a single click.
https://imgur.com/a/xxOcg8d
I would suggest that if the path found by the path planner is over some threshold it is treated as obstructed.