Make sure you don't skip the prolouge! A simple start, all you have to do is interact with the painting on the small shelf to the right of the bed in the very first room, the Nursery.

In the upper left main hallway, (2F West Passage, connecting the Archives, Changing Room, and Doll Room) there is a secret passage in the bottom left, simply enter it (there is also a Gem located here, further down).

First, enter the Archives and interact with the top-left bookshelf on the right side to read the data on live experimentation (this will also grant you the Code Memo).



After regaining control, re-enter the Archives and interact with the glowing object on the floor to pick up the Pendant. Make your way back to the East Hall (where you started the game in) and enter the Bedroom, the first room on the left. Approach the window, open the inventory ('X') navigate to the Key Items and use the Pendant ('Z' or 'Enter'). This will unlock the achievement and give you a Gem.

Story-related, can't be missed.

This achievement will unlock after getting an item from the Storehouse with Snowball.

In the Mortuary, interact with the head on the floor, then walk towards the door at the top until you hear the sound of a body falling off the table (it will be in the bottom right of the room). Upon approaching the body, it will get up and start following you. Guide the decapitated body to the head, once it gets there a scene will trigger, the achievement will pop, and you will get a Gem.

In the Passage (the room north of the Mortuary) simply talk to the old man.

Semi-story related.

After entering the laboratory for the first time and seeing the scene with Aya, Ogre, and Maria, interact with Maria and get the Room Key. Walk back to the Archives (in the left hallway, upstairs, door on the right, a ghost will also guide you to it) and use it on the door in the top left corner. Then, interact with the small bookshelf in the top left. Say 'Yes' to reading the diary.

Story-related, can't be missed.

In the Taxidermy Room (East Hall -> Stairs to Basement -> Outside Laboratory -> door on the bottom), pick up the Wood Bucket by the door. Examine the shelf on the far top-left (you will see an image). Start walking to the right until something falls behind you, turn around and pick it up to get the Eyeball Bottle.


(The bucket is located where Aya is facing in this screenshot)

Then, make your way to the Reception Room (the bottom left hallway from the Entrance Hall, door on the right). Walk through where the torn painting was on the wall, if there is a normal painting there, interact with it and move it. Go throught the passage, to the edge of the pond and use the Wood Bucket. After filling the bucket and Aya is shown walking with it, go back in the Reception Room and use it to put out the fire, then enter the fire place. Move the pile of wood, open your inventory and use the Eyeball Bottle. (If nothing happens, you must continue the story first, this is after aquiring the item that you use by pressing 'C'/'Shift', the chainsaw and finding a crying person in B1F Spare Room.) Aya will drop the bottle, you will hear the sound of glass breaking, now return to B1F Spare Room with the crying girl. Interact with the door. Go through the scene and enjoy your achievement with a Gem.

In B2F Laboratory, interact with the shelf in the top-right corner.

In B2F Laboratory, interact with the red book on the desk in the bottom-right.

In B2F Laboratory Inside (the door on the top left in B2F Laboratory) go up the stairs and use the chainsaw to cut the tied-up giant free.





Then, in B2F Laboratory, you can pick up a Gem, if you wish.

Enter the Hidden Passage from the Jail. Make your way through it until you exit again in another jail cell and make sure you pick up the Gem













Pick up the Jail Key on the table (move the barrel with 'Z'/'Enter') and use it (via inventory) on the jail cell with the experiment in it. Enjoy the achievement paried with yet another Gem.

Story-related, can't be missed.

Use your chainsaw on the hanging piece of meat in the B2F Cafeteria and pick up the Raw Ham.



Use the piece of Raw Ham on the stove (via inventory) and fry it. You must see the flashback of Mother reading to Aya before you can do this, to trigger this (first, make sure you save) then walk toward the door in the top right of the Cafeteria. After seeing that scene and another, walk back into the Cafeteria. Pick up the plate with the cooked ham ('Z'/'Enter') and bring it to the person sitting at the table.

Now, I cannot speak fully for this ahievement, due to there being no way to reset achievements and check what triggers them. How I recieved this achievement was by talking to Ogre in this room, the first time that you enter it and you are not attacked. (Your second time entering the room in one playthrough). This will probably trigger as long as you talk to him before solving the puzzle in the next room.

Firstly, as a warning, if you are poor at the arrow-key-pressing mini-game that happens when you are attacked, and unfamiliar with the "Abyss" room, the room on the side of a cliff, walk very carefully as pressing down will force you to complete the mini-game or its game over (right before a save point no less, that's no fun). Press only left until you are at the crow so you can save.

Now, throw that carefullness you just used right of the cliff... along with Aya.
To get this achievement, press the down arrow key to have Aya go off the cliff and start hanging. Wait for the mini-game to begin and pass it, this will cause Aya to completely climb back up and unlock the achievement.

Simply interact with the Doll in the Tunnel Big Passage toward the top left of the screen for this achievement. The creepy doll is located between the second and third doll that insta-kill you if you get in their line-of-sight.



There is also a Gem in this Passage, you can wait until you have finished with the Incinerator, as it will make travelling much easier and faster, you can get the Gem then.

For this achievement, all you need to do is first, solve the jigsaw puzzle in the Cultivation Room, then begin walking back towards the door, a drop of blood will fall from the ceiling, go back to the puzzle and view it for the achievement.

After getting the Incinerator Key, interact with the plant in the same room as the dog that swallowed the key, the plant will give you the bone and the achievement will pop.



You can visit the Cultivation Room again and use the chainsaw on the glowing plant to get a Gem.

IMPORTANT: You MUST receive the bone to get the "Dog's Best Friend" achievement.

NOTE: If you DON'T have the dog bone in your inventory, see the section before this one, "Special Gift".

Another note: I recommend waiting to do this achievement until after the event in the Incinerator Room, it will make travelling back much faster and easier.

To get this achievement, return all the way back to the room where Mom's Perfume was taken from you, and give the bone to the stuffed dog (via inventory), this will also give you a Gem.

Story-related, can't be missed.

This will trigger when Aya gets chased by Father.

NOTES: It is a requirement for "Aya's Future" that you get the true ending (The Promise) with all 21 Gems, if you need a guide, I recommend this: http://steamproxy.com/sharedfiles/filedetails/?id=768929118

Final Spoiler warning(s): this section and the following sections (Except "Aya's Future" and "Love Letter") are about the endings, so as you would expect there are some spoilers, but I've kept them as minimal as I can. I highly recommend waiting on reading these sections until at least seeing a dialogue box that comes up offering you a choice (because just me telling you what option to choose is a considerable spoiler, I'd say) and even until you reach whatever ending you happen to get to avoid the most spoilers. As long as you have your save before making a choice at the dialogue box, you're good.


You MUST select "Save Father" when the choice comes up, AND YOU MUST SAVE Maria by giving her the Bandage from the self. Then, complete the story as normal, you should get the achievements as you see the endings.

If you are having trouble:
- You don't have to spam Z until the doll blocking the door gets "killed" by Father with the chainsaw.

- When in the long hallway, the door at the end will be locked, hide behind the edge of the boxes and wait for Father to stand right on the opposite side of you and does his "charge"-thingy, where he becomes imoblie for a few seconds, while he does that, run back up to the door and flip the switch. Hide behind the columns and pop out every now and again (make sure you do it when you don't hear Father charge, or he will stay in the same spot and you will get nowhere) as you pop out, try to get Father as close to you as you can when he stops and cahrges the chainsaw, when that happens, sprint for the door and you make it.

Copy-paste spoiler warning from before:
This section and the following sections (except "Aya's Future" and "Love Letter") are about the endings, so as you would expect there are some spoilers, but I've kept them as minimal as I can. I highly recommend waiting on reading these sections until at least seeing a dialogue box that comes up offering you a choice (because just me telling you what option to choose is a considerable spoiler, I'd say) and even until you reach whatever ending you happen to get to avoid the most spoilers. As long as you have your save before making a choice at the dialogue box, you're good.

Story-related, CAN be missed while doing the "Love is Madness" (it may also be missed in the other Bad End "Beauty Preserved") ending where you grant Mother's wish.

Unlock it trough the True End. And possibly through IF? (The CG appears, but I do not know if it will count toward the achievement, if you do, let me know).

Copy-paste spoiler warning from before:
This section and the following sections (Except "Aya's Future" and "Love Letter") are about the endings, so as you would expect there are some spoilers, but I've kept them as minimal as I can. I highly recommend waiting on reading these sections until at least seeing a dialogue box that comes up offering you a choice (because just me telling you what option to choose is a considerable spoiler, I'd say) and even until you reach whatever ending you happen to get to avoid the most spoilers. As long as you have your save before making a choice at the dialogue box, you're good.

Choose 'Grant Mother's Wish' once the choice appears. Then, proceed normally like you did with "The Promise" (True End) (Don't forget to save Maria).

Copy-paste spoiler warning from before:
This section and the following sections (except "Aya's Future" and "Love Letter") are about the endings, so as you would expect there are some spoilers, but I've kept them as minimal as I can. I highly recommend waiting on reading these sections until at least seeing a dialogue box that comes up offering you a choice (because just me telling you what option to choose is a considerable spoiler, I'd say) and even until you reach whatever ending you happen to get to avoid the most spoilers. As long as you have your save before making a choice at the dialogue box, you're good.

Choose "Save Father" when prompted with the choice, do exactly as you did in "The Promise" (True End) EXCEPT ignore Maria. Do NOT save her.

After beating the game with the TRUE ending AND all 21 gems, IF should become available from the main menu.

To avoid small spoilers, I have not named any of the characters involved in this, but all you need to do is complete it and it is impossible to fail (as far as I know, at least).

All you need to do is walk to the Cafeteria, talk with the character there until they leave (when the first dialouge is finished they will walk and stop in front of the window, interact with them to trigger the next dialouge), then go to the Bathroom and talk to the character in there (you only have to talk to them once), then exit back to the Entrance Hall, walk up the stairs to the characters there, once you get control, go through the front door, and that's it!

To get this achievement, in the last room with the portal (don't enter the portal), there is a letter across from Ogre. Interact with it to unlock the achievement. I got this achievement on my SECOND playthrough of the game, as intended (hence why the achievement description says "on the second week"). For clarification, I completed the game and completely started a new file (selected New Game from the main menu) and played through it again back to that room. However, I have been told/seen multiple people say the letter appeared on their first playthrough.



Multiple people have also commented that the letter was not there on their second playthrough. Unfortunately, I have no and have seen no possible/confirmed answers or solutions as to why this is happening, so I only have suggestions.
During the second playthrough of the game, there are 4 letters/diaries (including the one needed for this achievement) that now appear in the game.
Their locations are:
[1] A diary in the 2F Bedroom, near Mom's belongings.
[2] A piece of paper in the B2F Passage, in a pile of books.
[3] A diary in the B3F Private Room, on the bottom-left table.
[4] This letter needed for the achievement to pop in the B3F Laboratory.
(credit to user 'Quote' for the other three letter locations from this thread: https://steamproxy.com/app/483980/discussions/0/350542683208575978/)

I WANT TO MAKE IT EXTREMELY CLEAR that I DID NOT interact with all of these new letters during my second playthrough, I just "speed-ran" the game to the B3F Laboratory and the letter was there, so this is all SPECULATION.

My suggestion(s) would be to interact with these new items during your second playthrough, if they do not appear, it could mean the game does not recognize that you are on the second playthrough, thus the required letter will not appear. Unfortunately, the only solutions I can think of that may work would be uninstalling/reinstalling the game, deleting your save data (and backing it up somewhere else, if you want), then replaying the game twice to hopefully have the letter appear. (Or maybe you'll get "lucky" and have it appear on your first playthrough).