The Kayran: Ostmurk is a Chapter 1 side quest in The Witcher 2: Assassins of Kings, part of the preparations for fighting the kayran near Flotsam. It starts when Geralt examines the beast’s mucus in the wrecked ship by its lair: Triss confirms the slime is both poisonous and magical, and the only reliable antidote calls for ostmurk, a blue moss that grows underground in damp places.
Geralt can hunt for the herb on his own or ask the elf Cedric, who points him to a cave behind a waterfall below the elven ruins. The cave is crawling with nekkers and ends with a greater rotfiend, so it is not exactly a stroll to the herb garden. With the ostmurk Geralt can brew a Mongoose potion against the kayran’s acid. The quest wraps up when the kayran dies, whether or not Geralt actually drank the potion, and rewards him with the Strong Stomach ability.
