There's a total of 58 "normal", visible from the very beginning, and 6 hidden achievements, which appear on the list only when you actually get them. Summing it up, there are 64 achievements to get in the Darkest Dungeon game, and most of them require quite a lot of work to get done.
Description: Reach the Estate
The first of many victories...
Description: Complete a quest.
Our victories are mounting...
Description: Complete 10 quests.
We are victorious, but at what cost...
Description: Complete 25 quests.
Discretion, my old friend...
Description: Abandon a quest.
Hint: to get it, you must abandon a quest by leaving the dungeon.
A strenous adventure comes to a close...
Description: Complete a medium quest
Hint: you must complete a medium mission.
A grueling adventure comes to a close...
Description: Complete a long quest
Hint: you must complete a long mission.
I've seen every corner of this ruined land...
Description: Complete a quest in all four regions
Hint: you have to complete at least one mission in Ruins, Cove, Weald and Warrens.
The first evil to fall...
Description: Slay your first boss.
Hint: to get it, you must defeat any boss in the game.
A team of hardened veterans...
Description: Start a quest with all four heroes of Resolve Level 6
Hint: you must start a mission with 4 heroes with the maximum (6) experience level.
And our training begins...
Description: Upgrade a Combat skill
Hint: buy any upgrade to your hero from the Guild.
It takes more than brawn...
Description: Learn a new camping skill.
Hint: you must unlock at least one camping ability from the survivalist.
A drink, a hand, and a companion...
Description: Treat a hero in the Tavern.
Hint: send one of your heroes to decrease stress in the Tavern.
A rumination, a prayer, and a confession.
Description: Treat a hero in the Abbey.
Hint: send one of your heroes to decrease stress in the Abbey.
Weeding out the weak
Description: Dismiss your first hero.
Hint: dismiss any hero to get this achievement.
A veritable crowd...
Description: Have one of each class on your roster.
The price we pay for sanity...
Description: Remove a Quirk in the Sanitarium
Hint: send a hero to the Sanitarium to get rid of a negative quirk.
Description: Lock a positive quirk in the Sanitarium.
Our equipment polished to a mirror finish...
Description: Fully upgrade the Blacksmith.
Hint: complete all upgrades in the Blacksmit..
Our techniques sharpened to a razor's edge
Description: Fully upgrade the Guild
Hint: complete all upgrades in the Guild.
The tavern my Ancestor once saw...
Description: Fully upgrade the Tavern.
Hint: complete all upgrades in the Tavern.
The abbey my ancestor once knew...
Description: Fully upgrade the Abbey.
Hint: complete all upgrades in the Abbey.
Restored to its former glory...
Description: Fully upgrade the Town.
Hint: complete every upgrade in every building in the city. .
Only the finest equipment will endure this torment...
Description: Fully upgrade a hero's weapons and armor
Hint: fully upgrade the armor and the weapon of at least one hero. .
Only masterful technique will suffice in battle...
Description: Fully upgrade at least four of a hero's skills.
Hint: upgrade 4 of hero's skills to the maximum level. .
A sobering visit with the departed...
Description: Visit the Graveyard.
Hint: simply enter the graveyard in the city.
A true champion emerges...
Description: Raise a hero to Resolve Level 6
Hint: get the maximum level (6) with at least one hero.
Description: Raise 4 heroes to Resolve Level 6
Hint: get the maximum level (6) with at least 4 heroes.
And we slew the evils that lurketh...
Description: Defeat 100 Eldritch enemies
Hint: kill at least 100 Eldritch-type enemies.
And we slew the abominations that haunteth...
Description: Defeat 100 Unholy enemies
Hint: kill at least 100 Unholy-type enemies.
And we slew the beasts that creepeth...
Description: Defeat 100 Beast enemies
Hint: kill at least 100 Beast-type enemies.
And we slew the men who were wicked...
Description: Defeat 100 Human enemies.
Hint: kill at least 100 Human-type enemies.
A killer of striking force and wit...
Description: Kill 50 enemies with one hero.
Hint: you must kill 50 enemies with a single hero, but it does not have to be done in a single dungeon, but in general.
The fiends must be driven back...
Description: Slay 1000 enemies.
Hint: kill at least 1000 enemies.
The end of the first year...
Description: Reach week 52.
Hint: to get this achievement, you must survive to the week 52, meaning that you have to complete 51 missions.
Two years of this...
Description: Reach week 104.
Hint: to get this achievement, you must survive to the week 104, meaning that you have to complete 103 missions.
Greater riches were never witnessed...
Description: Collect at least 20,000 gold from a single quest.
Hint: you should leave that achievement for late game (long, champion missions) during which it's a lot easier to accumulate the required amount of gold.
A collection of treasured antiques...
Description: Collect at least 30 heirlooms from a single quest.
More than a weary traveler...
Description: Walk 500 steps with one hero.
Hint: you just have to walk through 500 corridors (the smaller squares on the map, which connect rooms) with a single hero.
The first of many has fallen...
Description: Lose your first hero.
Hint: to get this achievement, you must lose at least one of your heroes - either in combat, or thanks to stress or a trap.
We all return to dust...
Description: Lose a Legendary (Level 6) hero
Hint: just like the above achievement, you must lose a hero, but this time with the maximum (6) experience level.
Sentimental relics from your forefathers....
Description: Acquire all your Ancestor's Trinkets.
Hint: you must gather all trinkets of the Ancestral rank. They can be acquired by completing quests, or found in chests and as loot drops from enemies.
Victory, such as it is...
Description: Complete the game.
In such haste...
Description: Complete the game within 99 weeks.
Hint: you must complete the game until you reach week 100.
Like lambs to the slaughter...
Description: Start a Darkest Dungeon quest with four heroes of resolve level 0
Hint: to get this, you must send 4 heroes with zero level to the Darkest Dungeon location.
Twisted and about to break
Description: Complete a dungeon with all 4 heroes afflicted
Hint: you must complete the mission with 4 afflicted (stress about 100 points) heroes.
The stresses were unbearable...
Description: Lose your first hero to heart attack.
Hint: when a hero gains 200 points of stress, he / she will have a heart attack, killing the hero instantly and giving you the achievement.
Gnawing hunger sets in...
Description: Lose a hero to hunger.
Hint: to get it, have a hero with low health (below 10% of his / her maximum) and when a hunger check appears select the option to starve the team, after which the hero will take damage and die.
No retreat, no quarter...
Description: First party wipe.
Hint: your entire team must be killed during a single mission.
What is already Dead Cannot Die
Description: Have a character survive 5 attacks at Death's Door in a single combat
Hint: cause the hero to enter the Death's Door (after reaching 0 health points) and then make him / her survive 5 attacks during a single encounter. You can increase the chances of survival with trinkets and quirks.
More blood soaks the soil...
Description: Party wipe on a boss
Hint: your entire party must die during a single encounter with a boss.
Description: Complete the game with default difficulty options
Hint: complete the game without changing anything regarding the difficulty level of the game.
Driven from this land...
Description: Kill all bosses.
Hint: you must kill all of the bosses, on all difficulty levels.
Description: Complete all Caretaker Goals.
Hint: the goals can be checked by entering the journal, or by checking the screen after you come back from a mission.
Description: Kill any boss with only one hero remaining.
Hint: kill a boss with the single hero remaining in your party.
Description: Kill any boss with a party of four afflicted heroes
Hint: defeat any boss with 4 afflicted heroes - heroes become afflicted when they reach 100 points of stress.
Description: Complete the game on NG+.
Hint: you must complete the game in the NG+ mode (unlocked after beating the game once).
On the old road, we found redemption
Description: Dismas and Reynauld Made it to the final Darkest Dungeon Quest
Hint: Dismas and Reynauld are the heroes you start your journey with. Make sure that they survive till the end and the achievement will be yours.
A terrifying figure emerged from the darkness...
Description: Slay a Shambler.
Hint: You must defeat one of the bosses, Shambler - how to do that can be found in the "Bosses" section.
That'll do, pig...
Description: Lose a hero to Wilbur
Hint: Wilbur is the small ping accompanying the Swine boss. Kill the boss and then let Willbur kill one of your characters .
We return to the worms of the earth...
Description: Lose a hero to a Maggot
Hint: Maggots can be stumble upon in any location - let one of them kill your hero and you will get the achievement.
Blocked from life...
Description: Lose a hero to an obstacle
Hint: get to an obstacle (where you must use a shovel to get through) with at least one hero with health below 10% and then get through the obstacle without using a shovel. It will kill the hero and give you an achievement.
Watch your step...
Description: Lose a hero to a trap
Hint: similar to the one above, but you must lose a hero to a trap.
Description: Lose all four heroes on a Darkest Dungeon quest.
Hint: you have to lose your whole party during the mission in the Darkest Dungeon location.