In Spider Cave, locate all the Dark Eco Crystals, and destroy them all. There are five Crystals.
The first is in the middle area of the first large room in the cave.
The second is near the three webbed jumpers that lead you to the cave with the giant robot.
The third is in the room with the Dark Eco pit. When you first enter the room, it is in the top left.
The fourth is in the same room. Head to the right, jump across the large pit of Eco, jump in the water, and swim down to the bottom to locate this crate.
The last one is the dark cave. You will find another body of water in here near the fourth light crystal. The crystal is at the bottom of this pool.