Here is the full list of all 40 The Forgotten City achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Reach Ending 4 of 4
Intimidate the creator of The Golden Rule
Reach Ending 3 of 4
Confront the creator of The Golden Rule
Reach Ending 2 of 4
Have Duli released from his cell
Find all three missing persons
Learn the true identity of the stranger by the river
Discover Underworld icons Sisyphus, Tantalus, Ixion and the Belide
Reach Ending 1 of 4
Help Galerius romance Equitia
Use Photo Mode
Pick up the sponge on a stick
Discover what lies beneath the city
Enter the upper cistern in an unconventional way
Save Ulpius's life
Find treasure using the golden bow
Solve Vergil's problem
Survive the Palace
Gild your first thing
Save Iulia's life
Save Fabia's life
Loop through time once
Allow Fabia to die in the collapsing temple
Enter a villa with a daring leap
Get rejected by Aurelia
Steal 2000 coins after the Golden Rule is broken
Free the captive and shoot her captor with your gun
Loop through time ten times
Finish the game without looping through time once
Reach the best ending with the smallest number of loops
Topple 10 peeled statues by kicking others into them
Talk your way through every possible confrontation
Trigger The Golden Rule by stealing 5 times
Read 10 different grafitti
Dodge 3 boulders
Die from hornet stings
Skip the city tour
Assemble as many people as possible in the Museum
Lie 10 times