class OuterWorld
{
    List<InnerWorld> houses

    override initialize()
    {
        houses = new List<InnerWorld>()
        construct each house, set the world = this on each one
    }

    override update()
    {
        foreach house:
            if player is inside the zone:
                FlxG.state = house
    }
}

class InnerWorld
{
    Rectangle zone
    OuterWorld world

    public InnerWorld(OuterWorld world) { this.world = world; }

    override update()
    {
        if the player is at the exit:
            FlxG.state = world;
    }
}