Here is the full list of all 14 InnerSpace achievements.
Cut down a hanging garden or Windcatcher.
Encounter the Sunfish.
Unlock your first airframe.
Collect your first relic.
While breaching the water from dive mode, pass over land before entering the water once more.
Encounter the Flock.
Encounter the Leviathan.
Encounter the Warden.
Encounter the Serpent.
Visit your companions.
Collect every relic in the Inverse.
Unlock all planes.
Fly into a world's sun.
Pollinate the Accordion Blooms in the Sunchamber.