On this page of the Horizon 2 Forbidden West guide, you will find information on how the fast travel mechanic works. We explained the requirements to unlock fast travel, whether it is free, and when the game may block the use of the fast travel option.
Unlocking fast travel
The fast travel mechanic in Horizon Forbidden West uses campfires, which are scattered throughout the world map. They can be found in uninhabited areas and in locations with NPCs. New campfire icons will appear on the map as you travel around the world.
You must first unlock each campfire by getting closer to it. Then it will be added to the fast travel menu. This means that you can use fast travel from the moment you unlock at least 2 different campfires.
Note - You can't use fast travel during the long prologue, which consists of two unique smaller locations. You can start looking for campfires only after reaching the main map - the titular Forbidden West.
Using fast travel
Fast travel is free - interact with a campfire and press the Circle. You must then select one of the other campfires from the world map and confirm to move to that location.
There is also a paid fast travel option from anywhere in the game world- without having to reach any of the campfires. You can do that by using Fast Travel Packs, which you can select from the Hunter's Kit. This can be a good method if you are in some very desolate place and do not want to make the long journey to the nearest campfire.
You can find fast travel packs in the game world, buy them from merchants or craft them yourself (you can get the ingredients by simply exploring the game world and hunting wild animals).
Temporary fast travel block
The game may block fast travel in certain situations. The main reason for this is the presence of enemies in the area, but only if they are hunting Aloy or fighting her - you must first defeat the enemies or escape them.
Another reason for not being able to use it is doing selected missions and extra activities, such as those that involve exploring a unique location without being able to leave until completing all objectives.