The Secret Realm "Nightmare" is different from the Night Cave Ghost Ridge; it’s a plot-driven Secret Realm with only one boss inside.

However, if you want to meet it, you have to find it on your own.

You need to follow the plot clues inside, gradually find the boss, and then eliminate it.

But many players lose their sanity during the search, attempting to alter the plot, and even when facing the final boss, they can't bring themselves to act.