To become a pirate legend in Sea of Thieves you’ll need to rank up each of three main factions in the game to level 50. Once you do, you’ll talk with the mysterious stranger that will give you a riddle to solve. “Through many voyages upon the sea, you searched to find the legends key. Now one last step to pass the tests, to find where Athena’s Fortune rests. Take this tune and make a sound, the secret lies near in the ground.”
This riddle requires that you play music in the tavern which will unlock a secret underground staircase that leads you to a new area for Pirate Legends. In this underground area you’ll find another faction for pirate legends that give you another 10 levels of quests to do which allows you to unlock new ship options and customization items. At this point, people are still waiting for updates from Rare to actually access some of the features that have been promised, like a legendary ship which allows you to sail from the pirate legend area.
The pirate legend quests are mixtures of the different types of quests with multiple chapters and are some of the most complex voyages that a crew will take on. Pirate Legend quests can give you the highest tier chests that you can get in Sea of Thieves.