There are no secrets in chapter 1

Hidden sound

If you wait in the classroom for a couple of minutes a sound of someone gasping will play.












Nun on the beach

On the second floor there is a nun you must play the music box too. Before playing it talk to her and you get to options, choosing the first option results in the nun simply standing on the beach, however the second option results in just the nuns clothes being on the beach.

While you get an achievement for this anyway, the master achievement didn't pop until I saw both versions

Edit: it seems that the nun will only appear on the beach after you get the other secrets.
Edit: WhiteWabbit seems to have activated this by just playing the music box and not talking to the nun, if you are having problems with getting the nun to appear then try this method.

Hidden eye

After drinking the water and passing out, head back to the coffin to see an eye painted on the wall.









Hidden crows

When you meet the lady that reads tarot cards, fill up the lantern before going to the area infront of the house that leads to the fog.
Once you have filled up the lantern go the the house and follow the man inside, then go straight to the garden of the house to see his shadow turn into crows and fly away.






Hidden message


When you enter the room with the grammaphone, simply turn it off and on again until a message plays.





Hidden books


When you encounter the man reading in the bookstore, stand between the piles of books to the left of him and you can select 5 books on the bookself to look at, these are fairly pixel hunty so move the mouse slowly over the bookself until you find all 5.


The names of the books are:

• The Horola by Guy de Maupassant
  
• The Great God Pan by Arthur Machen
  
• The Silver Key by Howard Phillips Lovecraft
  
• The Approach to Al-Mu'tasim by Jorge Luis Borges
  
• The Black Cat by Edgar Allan Poe

The Developers included these books as a secret because they inspired them when making this game.

Hidden sound
Enter the greehouse at the start, before you get the lantern and wait for a couple of minutes and you will hear the sound of glass breaking.










Hidden raven
If you wait in the bedroom after the window opens (don't leave the room at all) a raven will fly in a say "nevermore".

Thank you to The Ax-Man for creating this thread and causing me to go searching for the hidden secrets.

Thank you to the developers for making this wonderful game and giving clues to help me find the secrets when I was stumped.