If you go to Steam's Frostpunk's Achievement page:
http://steamcommunity.com/stats/323190/achievements You can easily recognize the secret achievements, because they don't have a description of what is required for them.
Here is their list:
- Banksy (
A New Home scenario - Deal with the graffiti peacefully)
- The Scientific Method, vol. 1 (finish the Automaton project)
- The Scientific Method, vol. 2
- Please, Sir, I Want Some More (when asked, give a child 2 food rations - typically happens if you enact Child Labor)
- Unknown Ship (Find the unknown ship in Frostland -
Refugees scenario)
- The Union (finish the
Refugees scenario, accepting all the lords and resolving the class conflict)
- Everybody Lived for Once (save both cities in the
The Arks scenario)
- Negotiator
- Sprinter (
The Arks scenario - reach New Manchester before Day 15)
- Golden Path
- My Turn to Speak