They seek the things that might be there.
They travel along the edge of dreams.
They explore the fringes of reality.
They know what lies beyond the shadows.
They have seen nightmares of flesh and fire.

“Seek new horizons and new experiences, and let nothing tie you down.”

Take all the weirdest things from the Cthulhu Mythos, the Umbra from Werewolf: the Apocalypse and from Lords of Madness for Dungeons and Dragons and you got a good idea of what you might encounter in Horizon Walkers.

I’m still in the early stages of brainstorming ideas and writing up potential campaign arcs, but it looks very promising so far.