Knuckles: Buried Treasure is the first Challenge Act of Sky Sanctuary Act 2 in the console/PC version of Sonic Generations. It is unlocked after clearing every Stage in the classic era and is playable only as Modern Sonic.
This Challenge Act stretches from the beginning of Sky Sanctuary Act 2 to the entrance hall inside the ruins. The Act basically has the same layout as the main Act, but with a lot of different structures.
To pass this Challenge Act, the player must reach the goal with at least thirty five medals in their possession. Having any less by that point will cause the player to fail the mission. To help find medals, the player is given a beeping sound, a directional arrow, and icons depicted above the medals to indicate their locations. However, the medals will always be buried in the ground, out of conventional reach. To reach them, the player must press / in their locations to call in Knuckles, who will then dig into the ground directly behind Sonic. The medals will then spray out of where Knuckles dug underground to be collected by the player. Sometimes, Knuckles can also dig up different Time Bonuses. Afterwards, Knuckles will jump out of his hole and disappear. Should the player call in Knuckles in the wrong spot, he will jump out of the hole in the ground and shrug before disappearing.
This Challenge Act is quite long and has several checkpoints. The first section is much like the beginning of Sky Sanctuary Act 2, except the Egg Robos are more spread out around the scalar. The next scalar in this section has cubic-built walls that lead to more Egg Robos, then to a set of Springs that lead to the next section. Noticeably, to the far end of the second section, there are flamethrowers that guard a medal location. To disable these flamethrowers, destroy the Egg Robo within them. From there, follow the path and use both Switches to form temporary platforms and ride moving platform to get to the highest point in this section.
At the start of the third section, the path splits in two, which will merge back together later. These paths can be reached by either going forward or to the right using the Jump Panel after the first bridge made of grassy platforms that collapse just after touching them. It should be noted that the path on the right initially consists of more collapsing platforms. Eventually, the player enters the penultimate section after crossing another path made of collapsible platforms that lead to the temple. To enter the temple, the player can either break through a window at the beginning of the third section or scale platforms to reach the main entrance further up. Inside the temple, the Goal Ring can be found on top of a fountain, which can be reached via a Wide Spring.
- A peculiar animation glitch makes Knuckles appear with two mouths on each side of his muzzle.
- This is the second Challenge Act that Knuckles the Echidna appears in.
- After completing this Challenge Act successfully and talking to Knuckles in the White Space as Modern Sonic, he will respond with, "A treasure hunter is useful to have around, right?"