Here is the full list of all 28 The Sinking City achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
Solve your first case in Oakmont.
Have your fortune read.
Go below the surface for the first time.
Use the intelligence archives in your investigation.
Press the button.
Betray the warehouse guard's trust.
Help the professor with his plan.
Challenge the horror of the Redemption Church.
Dethrone the patriarch.
Punish the upstart.
Ask the Imperial Wizard to show you a magic trick.
Study all the frescoes in the Temple of Dagon.
Have a ritual conducted on you.
Kill the old lady.
Finally commit the crime you were accused of.
Kill the priestess.
Kill the archeologist.
Defeat a little girl without playing fair.
Prevent the last self-immolation.
Leave the city and the world to their fate.
End the Cycle.
Restart the Cycle.
Agree to the experimental treatment.
Give an interview to the local newspaper.
Take Sidney's stash. You monster.
Uphold your agreement with Robert.
Humor a grieving mother.
Complete every challenge Oakmont has to offer.