Mobotropolis

Mobotropolis is a city on Sonic the Hedgehog's home planet that is home to both him and the Freedom Fighters. Among its more notably structures is Castle Acorn, ancestral home of Sally Acorn.

Worlds Unite
Mega Man, after being transformed into M'egga Man by Dr. Eggman and Dr. Wily on the orders of Sigma, was sent to attack Mobotropolis.