Valhalla Ravine is a recurring type of Event. They usually cost very little AP per level, especially on the lower floors, so are good for using up your final bits of AP before sleep or work or school.
Each level consists of three platforms, and the only enemy is a boss. Each floor will give you 10 Gems on the first clear, along with a one-time reward. Some of the significant rewards are weapon limit breakers, rainbow books for limit breaking characters, gold and silver gacha tickets, unique orbs (usually 2 or 3 per event) and wood and iron rings for leveling artifacts. Recommended strength levels range from 1,500 to 81,500 depending on floor, and usually increase by 1,000 power per floor.
Story[]
Fuginn has discovered a ravine with powerful monsters lurking inside. Lenneth went to investigate it and train there.