Tower of Remembrance

From the Soulcalibur Wiki

When Algol absorbed an amount of energy from the clashing of the cursed sword and the spirit sword (see his page for more details), he fashioned it into a body, weapons, and a massive tower, all based off the life he had eons ago. He named the spire the Tower of Remembrance, as it was a product of his memories, and nothing more than that—once the power absorbed had run out, he knew everything he created would vanish like a mirage. Thus, he waits in the Tower of Remembrance for the other characters, assuming one of them must have Soul Edge or Soul Calibur.

The tower has four stages:

Tower of Remembrance - Ancient Gate, the base of the tower, where all of the bonus characters are fought

Tower of Remembrance - Spiral of Time, one of the various chambers within the tower

Tower of Remembrance - Encounter, the summit of the tower when fighting Nightmare or Siegfried

Tower of Remembrance - Degradation, the summit of the tower when fighting Algol