This achievement is for completing the option bridges on each of the 5 islands in Camatuga. There are 10 bridges in total, 2 on each island. These bridges are off the main path of the island.
The bridges that are optional are:
Westlands
• Bridge 4
• Bridge 7
Central Mainland
• Bridge 4
• Bridge 7
The Ridge
• Bridge 2
• Bridge 6
Eastern Mainland
• Bridge 4
• Bridge 7
Tamassee
• Bridge 2
• Bridge 6
You will most likely get this simply by going through each of the 8 bridges for the other achievements anyway.