I want to import a terrain mesh I made in Blender into Unity, however Unity seems to fail to load it correctly. What could be the reason behind this and how can I fix it?
As per the comments, I'll repost this as an answer, so that the question has some closure.
That means you will have to recalculate your normals. Edit mode, A to select all of the faces, then Ctrl + N to recalculate the normals (outside).