Instructions
Complete Proon's Lair, the seventh level of the "Pit of Ill Omen" area. Board the boat and select the destination of Gnome's Island.
Save the Gnomes of Gnome's Island from the sea monsters. All eight gnomes must be saved to reach Gothic Castle, so save the game right before starting the challenge so you can reload if you fail. You may need several tries to succesfully time the sea monsters' attack patterns. You should also have plenty of health supplies in hand before you challenge them.
Speak to Babik after saving the Gnomes. He will offer you a boat ride to the secret area Gothic Castle, which is yours to explore--and try to survive.