Going through the tunnel on A1 was a cool experience. One side was green, temperate, and humid, then we cut through a tunnel, the other side was brown, dry, and hot. One minute of driving completely changed the microclimate. This was northeast of Zadar.
I know the one you mean! It feels like switching biomes. I went down that motorway with my parents when I was younger and althpugh the views were nice, it felt like it went on for ages.