Here is the full list of all 25 Down in Bermuda achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Collect all Relics and then pay a visit to the Relic Monument.
Complete all stats for Lava Island.
Help Milton to escape the Bermuda.
Complete all stats for Labyrinth Island.
Complete all stats for Forest Island.
Sort the sheep into their correct pens within 200 seconds of the gate opening.
Find all Orbs in the Lava Island.
Defeat the almighty Fire God and gain some new worshippers, Oonga Oonga!
Complete all stats for Shipwreck Island.
Unlock the mine cart in Shipwreck Island.
Complete all stats for Secret Base Island.
Solve the tricky orange liquid levers puzzle in Secret Base Island.
Complete all stats for Turtle Island.
Find all Orbs in the Shipwreck Island.
Shoot 50 cannon balls in Shipwreck Island.
Find all Orbs in the Forest Island.
Find all Orbs in the Secret Base Island.
Shoot 12 barrels in Secret Base Island.
Find all Orbs in the Turtle Island.
Pull up your explorer socks and complete the tutorial.
Help Milton to escape the Bermuda without opening a single Star Map.
Vanquish the Kraken in 7 shots of the cannon.
Complete the tile sliding puzzle in Labyrinth Island within 14 moves.
Inflate any puffer fish 10 times.
Open the door to Quack's hut three times.