I was trying to get a NavMesh working on Unity2D and was not able to get it working. Turns out navmeshes only bake on horizontal surfaces and the 2D perspective of unity has only vertical surfaces.
It is also explained in this video I found:
at around 10:30.
It would be nice if we could do everything on the 2D perspective, because if we have to rotate everything some of the tools of Unity2D stop working.