A POI (Place of Interest) is the red dot with a black cross marking something interesting, for example a natural cave.
Adding a POI marker. Edit
1. Fire up the World Editor.
2. In your object selection panel, go to records > poi. Select as an example [records>poi>greece>poi_starting_cave01. Place it and a large pillar will show up. This pillar is the POI on your map. It will say 'Natural Cave' if you use poi_starting_cave01.