Casinopolis

Casinopolis is a gigantic casino that appeared in Sonic Adventure as an action stage. Casinopolis is quite popular for the citizens and tourists of Station Square. The Casino only opens at night. This one woman seems to be addicted to it. Casinopolis is located in the Casino Area and has many bright lights. It is usually only open at night, and can be played through by Sonic, Knuckles, and Tails, as well as E-102 Gamma and Amy through the use of glitches.

Gameplay
The interior of Casinopolis is dominated by the presence of a massive Sonic statue, apparently made of golden rings. The statue is immediately visible when playing as Knuckles, but for Sonic to view his likeness, he must collect a huge number of rings and deposit them into the vault of the casino. This statue is extremely breakable since Knuckles can shatter it with one punch. Around the main floor of the casino are the vault, an information center, a large shower room, several small slot machines, and two pinball machines. The two pinball machines are quite different. The NiGHTS pinball machine is based on a five card (poker style) system, and massive ring bonuses are awarded based on card combinations gained while playing pinball (i.e. One pair, Two of a kind, Three of a kind etc.) while the Sonic themed one functions as a massive slot machine, with different levels of rewards gainable depending on the combination achieved.

The player is given three "balls" after entering either machine. If the player loses all three before gaining at least 100 rings, the machine automatically dumps Sonic into the large garbage dump built under the casino (The Dillapidated Way). Robotniks badniks seem to have taken up a patrol here, but if one is willing to brave them, massive rewards can be earned. Multiple pathways are available thanks to the massive fans built into the floor (apparently designed to blow garbage out of the way), and each path taken yields several capsules filled with ten rings each. Sonic can find several hundred rings down here, at least 400 of which are needed to complete the stage. Eventually, Sonic will discover a ladder that takes him up through a grate in the floor into the shower room of the casino, where he can wash away the filth from the garbage.

Sonic
Sonic's goal in this level is to deposit enough rings into the vault to form a golden mountain he can scale to reach the white Chaos Emerald sitting on a ledge far above.

Knuckles
When Knuckles travels through the stage, he gains access to the second floor, but subsequently loses access to the garbage, as he cannot activate the pinball machines. On the second floor, the most striking features are the presence of a large mechanical lions head, and model pirate ships complete with a robotic crew. His goal in this level is to find three shards of the Master Emerald, which may call for the destruction of the Sonic statue, as a shard may be hidden inside.

Tails
Tails is only allowed to play in the garbage area of the casino, racing Sonic through the neon lit pathways, trying to reach the silver Chaos Emerald before his best friend.

Trivia

 * Casinopolis was also mentioned in Sonic Heroes by Amy Rose; she compared it to a casino stage that herself, Cream the Rabbit and Big the Cat were in, despite this level not being accessible to her in her story-mode in Sonic Adventure (except for by the use of glitches or cheats).
 * There is an unused tunnel that can be accessed in the garbage using Debug mode.
 * This stage marks the return of the Sonic tokens.
 * There is also a mission which involves Sonic destroying Eggman's robots in the shower area.