POI = Point of Interest
These are things to walk around and see.
For example: There is a crashed spaceship near Orthos. It doesn't do anything, except serve as a bridge across a deep chasm. But it's cool to see.
There is also a very neat, huge tower south of Fort Pandora - also does nothing, but looks cool*
And there are plenty of others scattered across the world. Again, none of them do anything, but some do look very cool.
*There is a theory that, in the dome, in this tower, far out of reach of anyone, is where all the loot is kept. Of course, this is just a theory ;-)
~I