This is a Harvest challenge.
After Act 4, Niko, Master of the Depths provides introduction to delves.
Through waypoint, click to travel to the Mine Encampment:
The Crawler is used to navigate to undiscovered checkpoints, powered by Sulphite. The Crawler will automatically navigate to the chosen waypoint, providing light around it. If players move ahead of its path, it will greatly speed up to catch up to them and stops if players move too far away from it.
Go to Depth 20 or deeper and Complete a Delve Encounter
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Voltaxic Sulphite is used to travel to undiscovered checkpoints in the Azurite Mine. From act 4 onwards, zones can spawn 3 caches of Sulphite. Clicking on it will summon Niko to harvest it. The higher the zone level, the more Sulphite is gained. In maps, the amount of Sulphite received can be increased with map quantity. Nearby party members will also receive the harvested Sulphite. The Sulphite in maps can be increased with certain Scarabs.
Players can only hold up to a certain amount of Sulphite at a time. The maximum Sulphite capacity can be upgraded using Azurite. The amount of Sulphite needed to navigate from one checkpoint to another depends on the depth and the length of the path, up to a maximum of 1100 Sulphite per segment.