Here is a good example of a valley made by some megascan rocks. Nanite is handling the visuals awesome, but it’s impossible to add collisions to make them walkable at this scale.
For Nanite, better results are obtained when you duplicate the same mesh and assign a Collision Mesh. I hope this issue will be fixed in future versions.
I’m having a related issue where I’m trying to scatter foliage across a vast nanite landscape. Ideally I would detect the collision from the fallback mesh of the nanite landscape and return a location to place the foliage. Unfortunately the collision detection is very inaccurate. Even setting the “fallback relative error=0” doesn’t yield accurate collision detection.