To unlock this area, you need to complete the "Restoration" mission. The bridge built thanks to your help will lead you to Driftwood.
One of the lumbermen will ask you to clear the nearby islands of Hobbes . Follow the golden trail to reach the first camp of these strange creatures .
Kill them all and jump off the broken bridge into the water. On the shore on the left there's another group waiting to be taken care of . Once you're done, swim onto the opposite island . Get rid of the two groups there and jump off the nearby cliff. The last group is on the next island. Afterwards return to Robin to collect your reward.
Giftwood for Driftwood
Requirements: Pest Control
Richard will ask you to deliver a letter to the carpenter living in Silverpines . He can be found on the other end of the location, in a house to which the golden trail will lead you. Just talk with the man and the mission will end .