Sonata explores the Sunken Palace after fighting with Shadow in Tempest Forest. After finding out he's actually quite a good guy, Sonata feels obligated to help him find the Star Shard in the ruined caverns. After thanking Sonata for her assistance, Shadow suggests that she heads to Eternity Park, as she will be more likely to find somewhere there willing to help her locate the Chaos Emeralds.
Knuckles finds the Sunken Palace after finding a notebook in the ruined Twilight Hill village, detailing a previous explorers journey to the palace and how murals inside suggested a Chaos Emerald would be found there when reality would warp. Following the notes made in the book, Knuckles finds a portal to the Sunken Palace in Season Ruins, and searches for the emerald.
Sonic arrives in the Sunken Palace after defeating the Egg Hydra in Radiant Bastion and learning that Dr. Eggman's plan involves the Chaos Emeralds. He returns to Tails in vectopolis and learned of a Chaos Emerald in the depths underneath Angel Island. Sonic speeds off to find an entrance to the palace, with Eggman in hot pursuit. He meets with Knuckles, who had reached the palace proper from a separate portal leading into the coral gardens. Together, they search the palace for the Chaos Emerald, eventually fighting Eggman in the Egg Shark together. Having claimed the green emerald, they chase after Eggman, eventually ending up in the Inferno Canyon.
Sonic the Hedgehog
|Sonic the Hedgehog|
Sonic begins in the same place as Knuckles second section, but speeds straight through the main entrance instead of exploring the towers and corridors. Bursts of water will occasionally throw Sonic around rooms, often to higher ground. Spiralling water Slides from Sonata's stage also appear, and Sonic can jump between them like rails.
Eggman will occasionally smash into the palace, letting in torrents of water and quickly flooding rooms. These are usually hurried platforming sections across collapsing coral pillars as the exit of the chamber will eventually collapse. If Sonic fails to stop Eggman and reach the exit, he will have to take a detour outside the palace walls in the open ocean, where he will drown pretty quickly. When revisiting the level, Dream Shift can slow down the rising water levels to make this section easier.
Late in the level, Sonic will have to drain the water out of the throne room by going into side corridors and breaking the walls to shift the water. Knuckles will briefly take over in this section to cover the other weaknesses in the wall. The level ends in the drained throne room.
Sonata the Wolf
|Sonata the Wolf|
Sonata's level starts inside the Palace but she is almost immediately swept into a twisting tunnel by a water current into a cave, similar to tunnels in Labyrinth and Hydrocity. Most of it is spent speeding around on dry land, through water chutes and across water. Long water chutes twist around the cavern, throwing Sonata up and down and all around, and unlike most levels there is only one major path, though shortcuts and detours are still present. Spouts of water, marked by cracks in the rock, throw Sonata up high, and will raise the water level in the cave, causing some objects to float in the water higher. Shadow's assistance can be called upon to blow open some of the cracks, which is ultimately needed to open a passage housing a shrine, the star shard and the end of the level.
Knuckles the Echidna
|Knuckles the Echidna|
The Sunken Palace, despite being submerged for a very long time, maintains a pristine appearance. Without Eggman and Sonic's interference, the palace would display a minor case of leaking at most, though vines hang down in certain corridors and some rooms are completely flooded due to the walls collapsing.
The Coral Gardens resembles a huge, overgrown forest made of coral shapes in rainbow hues, in addition to cold, grey-purple rocks and more structured paths which appear to be part of the palace itself. Unusually high columns of rock have been decorated by shells, starfish like rocks and various colourful growths. Large anemones grow like flowers in areas, some pretty, some carnivorous and ready to engulf Knuckles. Areas of the garden appear to be a courtyard, though the remains have been covered by sand and coral almost beyond recognition.
The Trench Cave, where Sonata's level takes place, has a distinct Tomb Raider vibe, taking the appearance of a long-abandoned temple with torrents of water tipping in from above. While coral structures are still prevalent, they are dominated by patterned brickwork and dull purple stone pillars. The temple walls are mostly a dim purple colours, though green and turquoise patterned bricks fill in some of the gaps, occasionally branching off to form their own separate corridors. The Trench Cave deliberately evokes and warps memories of Hydrocity and Lost Labyrinth Zone in the background, showing what appear to be candle-lit displays in vague silhouettes and the remains of further temples in ruins.