Crystal Cave (クリスタル・ケイブ,Kurisutaru keibu?) is the fifth area of Sonic and the Black Knight. Eroded from the grassy rocks of Titanic Plain by underground rivers, Crystal Cave is a labyrinth of voluminous cavern systems. Giant, spiral stalactites jab down from the rocky ceiling from which Sonic can jump from, while on the cave floor, giant blue crystals and bioluminescent mushrooms grow within the subterranean detritus.
Although he should be making haste to complete Nimue's quests in order to free the kingdom from King Arthur's tyranny, Sonic is instead determined to answer a child's plea by preventing a crowd of villagers from becoming dragon food. After racing across Titanic Plain, the hedgehog arrives at Crystal Cave, where the beast has for now simply imprisoned the Arthurian folk.
Dashing through the caves and through hordes of Arthur's troops, Sonic sets the villagers free, and everyone escapes before the dragon returns to feed. Strangely enough, the felled beast is not justly slain until Sonic (or the other Knights) slays it before they reach the barrier stone.
Returning back from The Highlands with Nimue's deadline long past, Sonic finds the distraught child to tell her that her family is free, only for it to be revealed that said child is Nimue in magical disguise. The Lady of the Lake tells Sonic that by helping the "child", Sonic has fulfilled her last quest: offer compassion to those in need. Returning to her home in Deep Woods, Nimue agrees to at last tell Sonic how to defeat King Arthur.
Special Challenge: Rescue the townspeople - 250 followers
Rush Hour: Reach the goal without running into anyone - 100 followers
Rampage: Defeat 50 enemies - 350 followers
Collect Rings: Collect 100 rings - 250 followers
Chain of Rings: Collect 100 ring chains - 150 followers
Pass through the Goal: Reach the goal in time - 600 followers
Go for the Goal: Reach the Goal - 350 followers
Legacy: Reach the Goal - 200 followers
Items which can be acquired in the Crystal Cave missions include: Cursed Rapier, Moonstone, Tome of Jewels, Emerald, Lump of Iron, Beautiful Crystal, Rock Salt, Bronze Helm, Daisy, Steel Longsword, Cursed Longsword, Rusty Rapier, Aquamarine, White Ring, Rabbit's Tail, Expensive Broach