Realm of the lost

Four teenagers; Rowan, Maxine, Markus and Hoshi lived in a small town in America, recently the four graduated and the summer began. They all decided to go on a walk, and, find a strange cave. Hoshi desperately wanted to check it out, and Rowan agreed; despite Maxine and Markus stating it would be dangerous. Once the two begged and begged, and finally got their way; they went in. Finding a beautiful, shiny, gigantic, black crystal. Curious, they touched it; not realizing how much of a mistake it was.

When they woke up, they found themselves in a horrid realm only seen by the 'Heartless'.