So I have this idea that random encounters, such as gold hoarder maps/riddles, bounties, and reward from merchant alliance will produce a key fragment. The finished key would give access to a vault similar to the stronghold on a random island full of loot.
After getting the first fragment it will give maps, riddles, bounties, and merchant missions that will each have the chance for the next fragment so it is possible to have to do several different things before getting the next fragment.
(Optional) after completing the key when the player nears the island with the vault an army of skeletons will spawn with several captains that have to be killed to access the vault to use the key. Also a mark of some kind will apear in the sky of the island similar to a raid to tell people someone has a key and trying to complete a vault.
