This section of the Guide to Greedfall contains a walkthrough of the side mission The Cave of Knowledge, comissioned by Aphra.
How to start the quest?: A conversation with Aphra, after completing the Islander Knowledge quest.
Return to Vigyigidaw in Vedrad. Then talk to the people about The Cave of Knowledge. The cave is located in Darkred, Heart Gate. At the entrance of the cave, you will find an altar - search it.
Nearby, you will find a bunch of brigadiers. Talk to them and then make them go away - you can pay 100 gold, use charisma, or attack them. Now pick up the seed from the corpse and place it on the altar to reveal the passage further down the cave.
Explore the cave by heading to the highlighted points marked on the map. Finally, hide and eavesdrop on the conversations of the young natives.
Exit the cave and finish the mission. You will get 1300 XP and +3 reputation points with Aphra.