Here is the full list of all 12 Forward to the Sky achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Sky Tower explored
Final Chapter story revealed
5th Level explored
Chapter 5 story revealed
4th Level explored
Chapter 4 story revealed
Chapter 3 story revealed
3rd Level explored
Chapter 2 story revealed
2nd Level explored
Chapter 1 story revealed
1st Level explored