This was a narrow crack in the cliffs filled with large rocks
”
— How to Train Your Dragon
Madman's Gully is a valley stretching into the interior of the Isle of Berk from the beach at the Wild Dragon Cliffs. It is rocky and steep, and especially treacherous to traverse in the Winter.
Madman's Gully is the only way to reach Wild Dragon Cliff and the Dragon Nursery. The Novices and Gobber had to hastily get through Madman's Gully to escape the angry dragons accidentally awakened by Fishlegs in the Dragon Nursery, "the gorge they had climbed through a couple hours before".