Prison Hell Quest
From Realera Wiki
Name: Prison Hell Quest.
Location: Fermur.
Requirements: Completed Fermur Hell Quest.
Reward: Silver Trophy and 15 Pair of Hellflayer Horns.
Once you complete the Fermur Hell Quest, enter the teleport next to A Ghostly Gatekeeper
The path marked with colored lines in the order first white -> yellow -> blue -> purple.