Dark Hollow

Sonic and the Black Knight Previous area — Dark Hollow —

Dark Hollow is the final level of Sonic and the Black Knight where Sonic finds the final boss, Merlina as the Dark Queen. This is also where Sonic transforms into Excalibur Sonic by using the power of Caliburn and the 3 sacred swords wielded by the Knights of the Round Table.

Story
Sonic learns Merlina's purpose for committing such an act of devastation, transforms into Excalibur-Sonic, and battles the Dark Queen. Merlina is defeated and the Dark Hollow disappears.

Gameplay/Environment
The crimson-red area seems to be similar to the world in which Darkspine Sonic battled Alf-Layla-wa-Layla.

Trivia

 * The Dark Queen's monster form bears a strong resemblance to the King Arthur illusion fought by Sonic earlier on the game.