Fog of war is an experimental feature which initially hides areas of the map that have not yet been discovered by the player. This feature can be enabled from the “Experimental” section of your Game Configuration.Tiles, objects, and characters within a certain range and in the player's line of sight will become visible as the map is explored. Objects, such as doors, can be configured to block the player's line of sight. See the “Blocks Line of Sight” property on the Model Properties panel and the Set Entity Blocks Sight scripting function.
Fog of war will be built out more in future releases to allow customization of certain aspects, like the area of vision and whether or not explored areas will remain visible permanently.