A consumable item you can use to get to safety.
Return to Firelink Shrine or the last Bonfire you rested at with all your Humanity and Souls retained.
The Bonfires in this world are kept burning thanks to the Undead’s Bones. This bone was from someone that failed to complete their quest. The previous owner died wanting to go to a bonfire to rest so badly, his bones were enchanted with that primal instict, giving them this power.
Even in death, the hero seeks his rest.