The correct answer is - South.
The longest river in the world is the Nile River in Africa. The Nile has a roughly south-north direction, beginning from the Lake Victoria and ending up in the Mediterranean Sea. If someone is following the Nile River and it is by hiking upstream, that means that the person will be moving in southern direction. At first the hiker will face relatively flat terrain, but as it moves more and more upstream it will encounter a more rugged terrain, until it finally reaches the Lake Victoria.
