Battlefield

The Labyrinth of Time
This is where you obtain Spirit of Fire to reinforce your characters. The dungeon is categorized into three types: Strength, Agility, and Intelligence, ranging from 1 to 7 in difficulty levels. Each successive difficulty level is unlocked as you reach certain milestones in the Adventure campaign. Stamina is not consumed in this dungeon.

River of Fire
This is your classic "Gauntlet" mode found in most gacha games. There are ten stages in total with progressively harder difficulty, and the current HP of your characters are saved after each battle. This dungeon provides Draw Stones which are used to Draw your weapons in Forge, as well as other valuable resources such as Lava Essences and Equipment Reinforcement Stones.

Crack of Fate
Do not waste your stamina on this dungeon. It is a completely inefficient method to obtain Gold, and you will be much better off farming the Event dungeons instead. See Event Farming Tutorial.