This guide was written using erc's achievement guide, linked below. I would have been completely lost without it when I played the game.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2070546795
A couple quick notes before starting:

• At the time of writing this, The Sun achievement is bugged. In theory you need to play the whole game without ever picking up a lamp. In practice, it pops at the end of the game no matter what. Your call whether you want to try to gain it legitimately or not.
  
• Using chapter select clears progress for some achievements, such as The Hierophant, so you may want to avoid doing that.

Also, while I was writing this guide, TrueAchievements user Dwaggenienite posted their own guide. I referenced it for a couple parts of this one, so I think I'm obligated to link it here:

https://www.trueachievements.com/forum/viewthread.aspx?tid=1471555

Enter the room under the stairs (the door to the outside is locked, so don't worry about choosing wrong). Pick up the oil can (and the lamp if you want); use the oil can on one of the big oil jugs to fill it. Satisfy your curiosity by entering the cellar; this nets you


Head up the stairs to the top of the lighthouse. Turn on the record player for progression towards The Tower achievement. Turn the crank (you need to hold the interact key until it stops). Turn around and climb up the ladder. Use the oil can on the interactable area at the base of the big light.

Pick up your suitcase - it's just in front of you and to your left. Approach the lighthouse, and enter the house to your left as you get close. To your right, there's a place to put your suitcase. Open your suitcase and remove the medallion inside it. Use it on the chest to your left to progress The Magician achievement.

Take the key from the desk between the beds, and before leaving the room, look above the doorway and straighten the crooked cross to progress The Hierophant achievement.

In the room to the other side of the entrance, you can find a mop in the corner closest to the door. Take it and use it on the black puddle to progress The Emperor achievement. (You can put the mop back afterward; it automatically gets put back as soon as you leave the house anyway.)

Head to the top of the lighthouse (you can stop in the basement to retrieve the lamp if you'd like). Turn on the record player to progress The Tower achievement, and then go up the ladder to retrieve the oil can, which is on the ground. Go downstairs and refill it, then return and use it on the interactable area at the base of the big light.

Before going back down the ladder, use the door near it to enter the balcony. Then, leave the lighthouse and return to the beach. Approach the figure to get


Go back to the lighthouse and turn the crank, then go up the ladder to end the day.

Take the key, oil can, and optional lamp from the desk. Mop your floor again to progress The Emperor achievement (there are 6 black puddles this time, but they're all pretty close together). Head down to the beach and retrieve the medallion from the upturned boat; use it on the chest in the house to progress The Magician achievement.

Go to the lighthouse; on the way, take note of the small building (outhouse) behind your house. Fill the oil can and head upstairs. Take the cloth and use it on the black puddle, and turn on the record player to progress The Tower achievement. Go to the balcony and use the cloth on all the black marks on the glass. Head back inside and use the oil can on the interactable area under the big light before heading down the ladder.

You can't turn the crank, because the bags attached to it are gone. Pick up the remnants, then head outside and down the path until you reach a building to your left (the toolshed). Go inside and take the rope; head back up the lighthouse and use it on the dowel under the crank. (You can actually do this at any point while getting the bags, but I've found it's easier to do first.)

Go back to the toolshed and open the hatch to the left of it. Take a bag, carry it back to the lighthouse, and use it on the dangling end of the rope. You'll need to do this two more times. After you attach the second bag, once you're partway to the toolshed, you'll be yeeted into a kind of third-person mode as you take the perspective of something you don't control chasing the keeper you do control. If you die, you just restart this particular section, so don't sweat it too much. Turn right and run around the house and towards the outhouse to get


Look above you to find your exit. Retrieve and attach the third bag, turn the crank, and go up the ladder to end the day.

After a sequence where you can't really do anything, you wake up at home. Take the lamp if you want, then mop the floor again (5 puddles this time) to progress The Emperor achievement.

Go to the toolshed to get the shovel. There are ten mounds of dirt you can dig up with it.

• One is directly outside the toolshed.
  
• One is in the middle of the rocks on the cliff, to your right as you leave the toolshed.
  
• One is kind of between these rocks and the path, a little closer to the lighthouse.
  
• One is next to a rock behind the lighthouse; grab the medallion from this one before moving on. Slot it into the chest as you pass by the house to progress The Magician achievement.
  
• One is behind the house.
  
• One is behind a cluster of rocks to the right of the path coming from the lighthouse.
  
• One is by a single rock to your right as you continue down the path.
  
• One is directly between there and the start of the beach.
  
• One is by a cart to the immediate right of the path when it curves back.
  
• The final one (and the one you should dig up last) is on the other half of the island, in the middle of the trees.

As you approach the final mound, there'll be another chase sequence. I think the goal of this one is to make it to the house but I don't fully remember and the game let me skip it when I was replaying to make this guide. [ETA: When replaying again I was able to make it to the house and the game does accept this as a success.] Note also that you need to turn around before you start running; the sequence starts with you directly facing your pursuer. Regardless, after the chase sequence you can go dig the tenth mound up to find the key and oil can.

Assuming you dug up the tenth mound last, you'll get


If any of these are confusing, humito68's guide, while outdated in some ways, has screenshots for each mound location.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2075104683
Go to the lighthouse and fill the oil can. Turn the record player on; if you've progressed the achievement on all previous days, you'll get


Turn the crank and go up the ladder. Fill the light with oil. Go back down the ladder (go out to the balcony and back in first if the game won't let you go directly back down) and turn the crank again. Refill the oil can and use it on the light again. Head back down and turn the crank again, then go to refill the oil can once more. The oil jugs are gone, so continue into the cellar to find them. Refill the oil can and use it on the light to end the day.

Take the key from the desk. Start cleaning up the mess, including mopping up the puddle and the dead seagull. You can't do much without tools, though, so go to the toolshed to get the shovel, ladder, boards, hammer, and nails. Outside, use the shovel on the interactable patch of ground to get


There's a bit of the house just past that where you can use the ladder, so do so and climb to the roof. Use the boards, nails, and hammer to fix the roof, then head back inside. The final medallion has now fallen onto the kitchen floor, so put it in the chest to get a photograph, shotgun, two shotgun shells, and


Finish cleaning up the house, using the hammer where necessary. If you've progressed the achievement all previous days, once you're done (possibly only after you go outside when you're done? But if so, you can test whether you've finished correctly by going out and back in without consequences) you'll receive


If you'd like, go up to the lighthouse balcony and shoot the seagull for


but if you replay this chapter from the chapter menu later you can get the shotgun again without replaying previous days anyway, so it's your choice. If you do shoot the seagull, you can restart the level so you still have both shells (but note that 1) if you restart the chapter, you may reset some achievement progress and 2) you will have a chance to get more shells before needing the shotgun).

The oil can and lamp are both in the room under the stairs. Fill the oil can, turn the crank, and fill the light. Head back down the ladder and the stairs. You can't leave, so go into the room under the stairs again. A short cutscene will give you a reason to go into the cellar, so do just that.

In the cellar, walk forward until you hear noises behind you. As soon as you do, sprint ahead until you see an opening to your left. Go through that opening and jump down the hole to end the chapter.

You can only go in one direction at this point, so go that way, picking up the lamp if you so desire. When you hit a fork, go right, then turn left and go down a level as soon as possible. Head back towards where you came from, and you'll find a tunnel almost immediately to your left.

Down the tunnel is an object (an anchor?) covered by insects. Take the object and head forward down the stairs. Turn the crank to your left, then put the object on the chain the crank pulled up. Head back up the stairs and through the only available doorway, which is to your right. Take the dagger.

Go to your house and pick the cross up from under your bed. Put it back on the wall above the doorframe to progress The Hierophant achievement, then pick up the key from the bedside table. Go to the lighthouse, enter the basement, and try to leave again.

Head back the way you came to find the doorway to your right is open again. Turn right at the end of the tunnel, and then left when you get the opportunity. When you come to a fork, go left and retrieve a dagger, then double back and take the other path to some sort of body. Use the dagger on it and take the resulting object. Use the object on the strange thing hanging from the ceiling at the fork.

This opens another path, so go down it. Use the dagger on the statue, then take the dagger back. (I'm not sure if there's another way to progress things, but this is what progressed the plot for me, at least.)

Step onto the balcony, then go back inside and down the ladder. Leave the lighthouse; go to the toolshed and get the shovel. Continue to the other side of the island, where the mound with the key in it was. Dig up the mound you find there now, and open the casket, to get



Go back to your house.

Head back the way you came, then turn right and drop into the hole. In this next section, you have to navigate a maze and find the four medallions without getting caught by the monster, and then deposit them in a room with four anchors hanging from the ceiling.

General tips here are that the monster can see you from about one room away, the monster goes to different rooms in a specific pattern, and if it spots you, you may be able to escape it by hiding on a ledge.

When you enter the maze, pick up the medallion (this spawns the monster). Immediately turn left and go down two rooms, where you should find another medallion. Hide on a ledge and wait for the monster to show up, then when it's gone continue to explore. I was going to give further specific instructions but got turned around almost immediately, so I've opted to omit them rather than lie on the internet.

This mostly doesn't matter, though, because if you get caught enough times or have finished the level before, the game may have mercy on you and let you skip this level. There are no negative consequences to this, and in fact for doing so you receive


If you don't take the easy way out, once you're in the anchor room you should be safe as long as the monster didn't see you go into it. If it did, hide on a ledge until it leaves. Put the medallions on the anchors, then go through the path that opens up.

Interact with two bottles. One of them is on the place where you use the oil can, and the other is on the ground next to it. Go down the ladder and into the basement.

Load your shotgun if you haven't already, and head down the path. Turn the crank when you reach it. This lowers the platform you're on. When it stops, step off and take shotgun shells off as many skeletons as you can in the few moments of safety you have.

After the lights go out, you'll be trapped there with the monster. You have the option to fight, or to just jump in the pit to escape. You will need to do both to 100% the game (and if your goal is to minimize replaying, you should jump on your first playthrough so as to not reset a remaining achievement's progress).

If you choose to flee, try to get a hit on the monster before you go. It can hit you a couple times without killing you, so you have some time. If you manage to hit it before jumping, you'll earn


and whether you manage to get a hit or not, you'll get


If you choose to fight, you might end up reloading a few times because there is an achievement for killing the monster without getting hit. The restart level button will take you back to the beginning of this fight, and exiting and hitting continue will take you back to the basement just before this section.

If you stay generally on the move and keep circling the arena, you should be fine. The monster tends to stop for a few seconds after it charges, which is a good time to shoot it. When you successfully hit it, it makes a horrible noise and retreats briefly. This achievement will probably take a few tries, but once you manage it, it will pop:


and whether you manage it hitless or not, when you kill the monster you'll get


If you kill the monster, you'll end up in the church. There's an anchor you can interact with. Do so until nothing new happens, then leave through the door. Put the shotgun away. A cutscene will play and then credits will roll. There are two other endings, though, so we're not done yet.

If you chose to flee from the monster, the plot progresses to the next day. Look above you and hit the interact key until you're freed from the darkness. Go to your house, pick up the cross, and put it back on the wall. If you put the cross back twice before (and haven't reset your progress by using the chapter menu) you should get


Go towards the beds and a cutscene will play.

Go to the top of the lighthouse and interact with the dowel, then go to the bottom and interact with the three bags. Enter the basement and then the cellar. There's a bit of a maze here but don't worry about it too much, you'll eventually find the exit. There's a guy down here but I don't think you can actually catch up to him.

Then there are three chase sequences. In the first, your target is going to the house. You should be able to catch him by going a little to the right of him to cut him off.

The second target is going from the toolshed to the area where the church sometimes is. You shouldn't have too much trouble catching him, just keep sprinting.

The third target is trying to reach the lighthouse. Run directly toward the lighthouse and you should be able to catch him.

Go to the lighthouse and open the door. If you caught all three targets, you'll get


Go into the basement and move the oil jug to get into the cellar. Turn around immediately because you're pointed directly away from where you need to go, then just keep going forward until you're out of this place.

There's an achievement for catching this guy without being hit, so walk slowly around the arena until you see a tiny light. Run sort of diagonally towards it, and the keeper should shoot and miss you. Continue doing this until he's slow enough that you can catch him. If you manage to do this without getting shot, you'll get


You can restart the level if you get hit. Whether you manage it hitless or not, once you catch him you'll get

You'll end up in the church. There are candles in there corresponding to six achievements - The Hanged Man, The Emperor, Wheel of Fortune, The Star, The Lovers and The Moon. Once all six candles are lit, you can enter the hatch behind the altar.

Take the skeleton and go to the lighthouse balcony to find the shovel. Go back to the church area and bury the skeleton. This will unlock


Return to the beach, get in the boat, and leave the island. You will get


If you went the whole game without picking up a lamp, or if the achievement is still bugged, you should already have


and if you've gotten all the other achievements, you will receive


as the credits roll.