The last Cliff has an important part in the story. This is, of course, a fictional place, and there are no pieces of evidence of its real existence, only in the story. According to the book, there is a hidden staircase behind the cascades, that leads to the top. "Can you imagine someone climbing a wall like this?"
This is the first version of the map:
In the first version of the map, the waterfall comes from another river, not from the Euphrates and it had to be changed days before the launch of the book, to fit the story: