SPOILER ALERT!!! READ THE WHOLE SERIES BEFORE READING THIS!!!
We all have read about the other side.
We all at least have an idea that these stories are real.
What is the other side? We can have a lot of theories, ideas which may be a great amuse bouche to great achievments - but we all know we have to see other refrences and ideas about the other side, not only by readers of The Secret Series!
And now, for the refrences (tell the community in the comments section the ones you found, and I'll add them to the post. I will mention your username, if you'd like.):
The Doors - Break On Through (To The Other Side) (posted by me)
A great song. The Doors made it while drugged on LSD. They did not vanish like Pietro did, but they may have been on a trip to the other side...