Treasure maps like in Red Dead Redemption.
Treasure maps would start as a drop from champions.  That have clues to a small hidden stash.  The small hidden stash would also have another map with more clues to follow.  That would lead to another small stash or one big stash.
Treasure maps-Drop from champions and small hidden stashes 
small stash-drop one treasure, gold, rare items 
big stash-guarantee rare, exotic
RNG would determine if map leads to a small or big stash.  But the player would not know which it is.
*Players can only have one map per character at a time.  No new maps will drop until
*Destroying a map ends the treasure hunt.
*Treasure ends when a big stash is found. 
*finding treasure maps are endless quests.
*Maps are soulbound, must be that way for this to work.