I ran into an issue where I could move units from one tile to another, but I couldn't come back the same direction. Maybe there is a cliff I that I can travel down, but because I'm moving from a district to a northern tile, I can't tell what the terrain is. 

In the attached photos, I was trying to move a unit from Kis to Babylon. I had to go round a mountain to get to Babylon, but going to Kis, I can follow the roads. Very weird.