Here is the full list of all 49 Call of Cthulhu achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Find 20 hidden items
Read all the books of unholy knowledge
Invoke Cthulhu!
Choose all the replies in R’lyehian
Refuse to take part in the ritual
Discover all the murals of the disappeared tribe
Piece together Margaret Wyckwood's memoirs
Save Mitchell
Push Irene Sanders to the limit
Discover all the small blue bottles
Use the globe to open the secret passage
Be the plaything of an hallucination
Successfully carry out the counter ritual
Refuse the ritual
Chat with a vision
Open the sailor's chest in the whaling station
Enter the beast’s den
Kill 5 inhabitants who are being controlled
Kill or spare Bradley
Escape your fallen territory
Make the suspects talk by using a heavy hand
Accept the revelations
Save Drake's life during the fight with the creature
Banish the creature for good
Never drink
Lay your hands on Algernon Drake's treasure
Find occult items
Find Sarah Hawkins
Fall into Fuller's trap
Meet Algernon Drake and accept his help
Learn the secret of the Scylla
Heal all the patients
Read the Necronomicon
Banish the Dimensional Shambler
Banish the Dimensional Shambler using only one dagger
Accept to read an unholy book
Inspect 50 items
Meet Francis Sanders
Make a deal with a crazed inmate
Take part in the ritual in the caves
Fall into the sacrificial pit
Discover the mansion’s secret passage
Reach the level of Expert in a skill
Convince the caretaker to help you
Explore the memories of the Hawkins family
Get driven to the Hawkins Mansion
Deliver liquor to the sailors
Accept the Sarah Hawkins case
Fail a skill test