Here is the full list of all 23 A song in the void achievements.
Complete the first island
Complete the second island
Complete the third island
Complete the fourth island
Complete the game
Play the second ending of the game
Collect all energy cells on Island 1
Collect all energy cells on Island 2
Collect all energy cells on Island 3
Collect all energy cells on Island 4
Discover Tortuga
Have a talk with a Vulture
Enter the Dragon's lair
Meet a giant spider
Ride a flying mammal
Jump in the water...
Some like it hot...
Jump, you know you want to
Get too close to a spider
Become worm food
Ride a turtle
Play with dandelions
You're a bird, a plane, a...