C2080 Disappeared Sixth Floor

On the fifth floor, down is the first floor, up is the fourth.

On the first floor, he walked up to the fifth floor, and down to the third floor.

The sixth floor didn't seem to exist.

But from the window, they could clearly see that the highest floor of the castle was seven floors, so there was a sixth floor.

But why?

He couldn't go up to the sixth floor?

He was clearly right in front of him