Leather is one of the many materials that you can find and collect within V Rising. It can be used for many different reasons, including being able to upgrade the Castle Heart.
The earliest location in which you can find the Leather is over at the Bandit Trapper Camp. This area becomes available during the Keely The Frost Archer mission quest.
The Bandit Trapper Camp is located north east of the Farbane Woods. The Leather is one of the many materials that can be found and located here
By completing the Keely The Frost Archer mission quest, the Tannery Tailor workstation will drop and then become available to us. With this workstation we will then be able to craft and create Leather.
With the Tannery now available to us we can then return back to our base and set up our new workstation.
Keep in mind that in order to create Leather we will need to acquire Planks and Animal Hide