The Fast travel system is a mechanic introduced in The Witcher 3: Wild Hunt due to the significant increase in explorable areas. It enables Geralt to "teleport" between two already discovered signposts, or to a discovered harbor if he is sailing on a boat. Geralt can also jump to a signpost located in another game region and this takes more loading time.
Additionally, if Geralt wanders to the very edge of the explorable game areas, the map interface will appear allowing him to fast travel to any signpost or harbor (if he is at sea).
Tutorial description Edit
Signposts allow for Fast Travel between distant locations. To Fast Travel to a location, you must first visit it normally. Only then will a Fast Travel marker appear on the map for that location.