After locating the entrance to Dr. Eggman's pyramid base, Sonic and co. find that the door to a rocket that will take them to the Space Colony ARK, where Eggman is located, is locked. Sonic persuades Knuckles to find the three keys to the door so they may proceed.
The first goal to this level is different from all the other levels belonging to Knuckles. Instead of finding Master Emerald shards, he's actually looking for three keys to unlock a door to find the rocket to take the team to the Space Colony Ark to stop Eggman. This level, like some others in the game, has quite a few ghosts in it. King Boom Boo is the following boss after this stage, and Egg Golem following right after that.
Collect 100 Rings
After grabbing the six Rings in front of Knuckles at the beginning, head for the blue section of the stage. Play the Mystic Melody at the Ancient Ruin to make fourteen Rings appear. From there, keep heading for the blue section, where a Magnetic Shield will be in the room just after the metallic hallway. By arming Knuckles with this power-up, collecting the remainder of the Rings will be much easier.
Find the Lost Chao
Play the Mystic Melody atop the Ancient Ruin on the floor of the Pyramid Core, and dive into the water when the hatch opens. As the player dives down, they should see a closed door. Then, swim to the other side of the room and find the Hourglass. Flip it and make a beeline for that door, because it closes quickly. Once the player has made it through, they should swim across one hallway where two robots are firing, and then another hallway lined with Boos. Once the player enters the large cavern, they should swim up almost immediately to emerge from the water.
Climb out to see an Hourglass in the alcove above. This opens the door directly above it, and behind that door is the lost Chao. The only problem is that the door juts out a bit, so the player will not be able to climb straight up. Instead, flip the Hourglass and work the way around as quickly as possible before the door closes.
Find the 3 Keys within 5:00
This stage can be a bit confusing, so do not be afraid to use a Hint Box for hints.
Clear Hard Mode
To find the first key, begin by digging through the painting found in the hallway between the red and green sections of the stage. The player will thus enter a large room with an Hourglass on the opposite side. The player then has to flip the Hourglass to make platforms slide out from the left- and right-hand walls. After that, they should jump onto one of them and smash the Iron Containers to reveal another Hourglass. Next, the player should flip that Hourglass, making the large hatch in the center of the room open. Now, the player should quickly run down and dig into the dirt there to reveal the first key.
For the second key, the player must head for the location of the lost Chao. Once the player reaches the large cavern, however, they must not swim up to the room above. Instead, they must swim straight ahead, where they will find the key behind an alter. However, they must beware of the Unidus hidden behind there as well.
After obtaining the second key, the player must swim up into the room where they found the lost Chao. A giant Weight falls should fall on the player, and close off the entrance to the water. First, the player must climb straight up and hit a Switch to raise the weight again. After that, they have to flip the Hourglass in the alcove below and quickly dive back down. For a brief time, the key is revealed in an alcove of the second step from the bottom.
The Level Up Item in the stage is the Hammer Gloves, which allow Knuckles to break open iron boxes. The Hammer Gloves can be found in the hall from the first room behind a wall of crates.
Oddly, despite being inside Eggman's Hidden Base, the Egg Beetle is not used, unlike Rouge's stage, Egg Quarters where it was used.
This can possibly be explained by the fact that Rouge was breaking into the base while Eggman was gone, while Sonic, Knuckles, Tails and Amy are breaking in while he's still there (which can be deduced from the fact that Eggman shows up in person after the King Boom Boo boss fight). Thus, it makes sense that he might disable the Egg Beetles while he's inside his own base.
This stage is similar to Rouge's Egg Quarters, yet the Egg Quarters is Rouge's second stage while the Death Chamber is Knuckles' fourth stage.