There are a total of seven achievements all history related so if play the game till the end you should have gotten them all!

Met by moonlight

You get it when you first met Althea


Under her spell

Gotten after the pinky promise with Althea


Step into the circle

Gotten when you enter the candle circle with Althea


Bathed in silver

Have a picnic with Althea


Witchcraft in her lips

kiss kiss fall in love


Demystified

Read the book in the attic

Hidden Achievement
Charlotte

Find out the truth and that she is not actually a ghost lol

And thats it!