In Mega Man 4, Mega Man can enter the citadel after defeating the game's eight Robot Masters and selecting Dr. Cossack's portrait in the centre of the stage select screen.
The citadel is depicted on the map screen as a castle with blue outer walls, green inner walls and a central onion dome tower that evokes those of Saint Basil's Cathedral. Like many fortresses in the Classic era, it is divided into four unnamed stages, each with a boss at the end.
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