In order to get this achievement you have to find the campfire location on Balboa Island and pick up all five of the notes around it. The campfire is at the base of the cliff that relay station 6 is on top of and you can see station 6 from the campfire.
This is a simple guide to help you unlock the tower code at the top of the tower on Tangaroa Island. You May Also Like: Raft - Building Raft on Single Foundation. Raft - Infinite Equipment Durability.