The 'hello darkness story' might be a creative narrative. It could be about a character who is in a state of despair or solitude, symbolized by 'darkness'. The story could then revolve around their journey within this 'dark' state, perhaps finding a glimmer of hope or self - discovery while in it. For example, it could be like a person lost in a forest at night (the darkness) and their struggle and growth during that time.
I have no idea who created the 'hello darkness story' as there could be many different stories with this name. It might be an indie writer, or it could be something created by a local storyteller.
The story could be significant in terms of the cultural impact of Simon & Garfunkel's music. 'Hello Darkness, My Old Friend' has been used in many movies and TV shows, which shows how it has become a symbol for a certain type of mood. If Art Garfunkel has his own take on it, it might be an extension of that, perhaps a more personal exploration of those feelings within the context of his own artistic journey.
Some fanfictions may use the 'hello darkness my old friend' concept in a more metaphorical way. For instance, it could be about a character's relationship with an old, perhaps not so positive, part of their past that resurfaces. This could be an old habit, an old acquaintance that brings back memories, or an old way of thinking that they thought they had left behind but now has to deal with again.
Some common themes could be mystery. The castle itself might be a source of many secrets waiting to be uncovered. Another could be adventure as characters might explore the different parts of the Darkness Castle. And there might also be a theme of self - discovery as the characters face various challenges within the castle.
One popular character could be a rogue - like figure. This character is sneaky and resourceful, able to navigate the castle's hidden passages. Another could be a powerful sorceress who has her own motives for being in the castle. Also, a young apprentice who is learning about the castle's magic and trying to prove himself would be a common character in the fanfiction.
They might get really excited and start comparing it to their own experiences in the Trolls world. Maybe they'll laugh at the funny parts or feel inspired by the creative interpretations in the fanfiction.
As I said before, I'm not sure if there actually is such a novel. So, it's hard to say where you can find it. If it does exist, you might start by checking with local independent bookstores. They sometimes carry more unique or less - known titles.