What are Fox Dens in Ghost of Tsushima?
Fox dens are home to useful foxes that will improve your charm ability. If you come across a fox lair in Ghost of Tsushima, follow the fox and it will lead you to a Inari Shrine. Inari shrines can be quite difficult to find without the help of a fox, so it's best to find and follow the fox in a fox pit rather than trying to find the shrine on your own. Praying in an Inari shrine will give you a additional charming location, allowing you to equip more charms at a time. Charms can have a lot of useful benefits, such as increasing the damage of certain weapons or making you harder to spot. Finding fox dens and Inari shrines will allow you to customize your build in Ghost of Tsushima and give you much greater control over your playstyle, so don't ignore them if you come across one.
Generally, if you notice a animal trying to get your attention somehow in Ghost of Tsushima, it's probably best to follow him. The game does not use traditional markers and waypoints, so it relies on elements of the game world to convey information to you. Foxes are one thing, but there are also yellow birds that will fly near you, indicating that a useful resource or item is nearby. Following these golden birds can lead to new vanity items, bamboo strikes, hot Springs, or other useful stuff, so don't ignore animals that just seem a little out of place.
