From Sonic Retro
White Acropolis is a stage in Sonic the Hedgehog (2006) for the Xbox 360 and Playstation 3. As with other levels in the game, it features in all three of Sonic, Shadow, and Silver's stories, although the characters fight their way through the area at different times and for different reasons.
Surrounding Dr. Robotnik's main base of operations in Sonic '06, White Acropolis is a snowy (and avalanche-prone) mountain range, with scattered pine trees rising over frozen lakes and bottomless chasms. Being Eggman's fortress, the place is swarming with Egg Gunners and other robots, as well as towering searchlights and laser fences on every approach. The Doctor's prison complex and "Solaris prototype" time machine are housed here, although the Egg Carrier's hanger lies elsewhere, in Aquatic Base.
Shadow's opening sequence sees him contacted by GUN HQ, to respond to an SOS signal from one of its agents in White Acropolis. Storming the place in typical explode-y fashion, the black hedgehog sweeps through veritable armies of Egg Gunners to fulfil his mission.
Shadow starts off running down the same slopes that Sonic later snowboards. At the same time, the GUN agent he's been sent to rescue - who turns out to be Rouge the Bat - is attempting to sneak out on her own by fleeing along the canyon walls. The final segment sees Shadow driving an Armed Buggy to blow up enough of Robotnik's searchlights that they can escape safely.
After the boss, Rouge reveals that she was in the base to steal the Scepter of Darkness from Eggman. Shadow and the bat make their escape via a teleport device to Soleanna New City, after which Rouge asks Shadow to escort her to the GUN rendezvous point in Kingdom Valley.
S Rank Tips
It is possible to get the S Rank requirement in Shadow's mission on level score alone, and go over 20,000 points beyond the requirement with proper ring bonuses. To accomplish this, three key things must be kept in mind:
Don't forget the three rainbow rings in the first section either. Or easily collapsible towers worth 10 points.
But, this is very time-consuming (kiss any time bonus goodbye for taking around 20 minutes to do this), and the fact that one death wipes your entire score up to that point will be even more frustrating when almost a half-hour of progress disappears into the abyss you just fell down in when getting to that searchlight by the gates. So be careful there.
But there is an alternative:
Distracted by the boss fight against Silver in Soleanna Castle Town, Sonic is unable to prevent Eggman from recapturing Princess Elise. Fleeing the city, the fat scientist leaves a holographic message with Knuckles, offering to release the Princess if Sonic brings the blue Chaos Emerald to his base in White Acropolis. Even though Tails correctly diagnoses the ransom as a transparent trap, Sonic speeds off to the hideout, intending to simply break Elise out.
The level starts with Sonic snowboarding down the mountain slopes, eventually being pursued by a giant rolling snowball. The subsequent standard platforming section includes a period controlling Tails, who must fly over various impassable chasms in order to open a blast door for Sonic to progress.
Team Sonic eventually breach into Eggman's facility, discovering the scientist and Elise on the other side of a glass barrier. As per Eggman's ransom, Sonic places the blue Chaos Emerald inside a machine as instructed - at which point the fat man flips a lever, activating his time machine and sending the heroes on a blind jump into the far future: to Crisis City.
Blaze finally finds Silver moping around in Soleanna New City after Amy foiled his attempted assassination of Sonic. After a brief sermon from the cat on the acceptability of murder, they set off for Dr. Eggman's base - deciding that if Sonic's looking for the fat man, said fat man's hideout should at least teach them something about their adversary.
White Acropolis starts with Blaze smashing up the robots on the outer mountainside. Silver's sections then see him floating through the canyons and across Eggman's fortified snow plains, eventually reaching the base. After defeating Egg-Genesis, the duo recover the blue Chaos Emerald which Sonic deposited inside the time machine. Subsequent cutscenes show Elise and Amy (the hedgehog having also snuck into White Acropolis to find Sonic) escaping from Eggman's prison complex.