Casinopolis

Casinopolis (カジノポリス) 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. It 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.

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 fragile, as 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 pinball machines are quite different from each other; the NiGHTS machine is based on a five card (poker style) system, and large 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 giant slot machine with different levels of rewards gained, 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 drops Sonic into the large garbage dump built under the casino (The Dilapidated Way). Dr. Eggman's 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 due to the large 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 leads 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 at least 400 rings into the vault by breaking the machines and playing pinball. This will form a golden mountain which he can scale to reach the white Chaos Emerald sitting on a ledge far above.

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

Knuckles
When Knuckles travels through the stage, he gains access to the second floor, but subsequently loses access to the garbage area, as he cannot activate the pinball machines. On the second floor, the most striking features are the presence of a large mechanical lion's 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.

Sonic Pinball Party
Sonic Pinball Party is set in Casinopolis.

Trivia

 * Casinopolis was also mentioned in Sonic Heroes by Amy Rose; she compared it to Casino Park, a stage that herself, Cream the Rabbit and Big the Cat visited despite not having access to Casinopolis in her story-mode in Sonic Adventure (unless glitches or cheats are used). This may be explained by the fact that she lives in an apartment in Station Square, and at some point during her time there, she may have visited the casino.
 * 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.
 * In the original Japanese version of Sonic Adventure, there is a neon sign depicting a cowgirl in Knuckles' version of the stage. It was removed in later versions due to its rather provocative nature, showing the cowgirl half-dressed and using alcohol. O_COWGIRL.png
 * Casinopolis appeared in Sonic X.
 * Through the use of various glitches, it is possible for E-102 Gamma and Amy Rose to enter Casinopolis.
 * This level marks NiGHTS' first appearance outside of NiGHTS' home series and the first of many NiGHTS appearances in the Sonic series.