This can be one of two places

The first being a calm and peaceful kingdom

Mobotropolis

This is ruled by the Acorn royal family

You're bound to run into them eventually here

Or you can go for a dystopian dictatorship

Robotropolis

If you chose Robotnik for your roleplay, this is what you'll get if he takes over

A city crawling with SWAT bots and Robians

If you liberate the city, it will return to Mobotropolis

The choice is yours