public sealed class Version01_MutableLocation
{
    public string Name { get; set; }
    public string Description { get; set; }
    public Version01_MutableLocation North { get; set; }
    public Version01_MutableLocation South { get; set; }
    public Version01_MutableLocation East { get; set; }
    public Version01_MutableLocation West { get; set; }

    /// <summary>
    /// This instance method is a pure function, but it's dependency - the class instance - is referenced via the 'this' operator
    /// </summary>
    public string Narrate()
    {
        string narration = string.Empty;

        { // This block constructs the string that is the description
          // of the location that is displayed onscreen to the game player.
            string northExit =
                null != this.North ? " North" : string.Empty;

            string southExit =
                null != this.South ? " South" : string.Empty;

            string eastExit =
                null != this.East ? " East" : string.Empty;

            string westExit =
                null != this.West ? " West" : string.Empty;

            string allExits =
                string.Empty != string.Concat(northExit, southExit, eastExit, westExit)
                ? $"{Environment.NewLine}Exits:{northExit}{southExit}{eastExit}{westExit}"
                : string.Empty;

            string separator = new string('-', this.Name.Length);

            narration =
                $"{this.Name}{Environment.NewLine}" +
                $"{separator}{Environment.NewLine}" +
                $"{this.Description}{Environment.NewLine}" +
                $"{separator}" +
                $"{allExits}";
        }

        return narration;
    }

    public static void Main(string[] args)
    {
        var kitchen = new Version01_MutableLocation();
        kitchen.Name = "Kitchen";
        kitchen.Description = "You are in a messy kitchen.";

        var library = new Version01_MutableLocation();
        kitchen.Name = "Library";
        kitchen.Description = "You are in the library.";

        var office = new Version01_MutableLocation();
        office.Name = "Office";
        office.Description = "You are in the office. There's a computer on the desk.";

        kitchen.North = library;
        library.South = kitchen;
        library.North = office;
        office.South = library;

        Console.WriteLine($"{kitchen.Narrate()}");
        Console.WriteLine($"{library.Narrate()}");
        Console.WriteLine($"{office.Narrate()}");
    }
}

public sealed class Version02_MutableLocation
{
    public string Name { get; set; }
    public string Description { get; set; }
    public Version02_MutableLocation North { get; set; }
    public Version02_MutableLocation South { get; set; }
    public Version02_MutableLocation East { get; set; }
    public Version02_MutableLocation West { get; set; }

    /// <summary>
    /// This static method is a pure function, and all of its dependencies are passed in the function's argument list.
    /// </summary>
    public static string Narrate(Version02_MutableLocation location)
    {
        string narration = string.Empty;

        { // This block constructs the string that is the description
          // of the location that is displayed onscreen to the game player.
            string northExit =
                null != location.North ? " North" : string.Empty;

            string southExit =
                null != location.South ? " South" : string.Empty;

            string eastExit =
                null != location.East ? " East" : string.Empty;

            string westExit =
                null != location.West ? " West" : string.Empty;

            string allExits =
                string.Empty != string.Concat(northExit, southExit, eastExit, westExit)
                ? $"{Environment.NewLine}Exits:{northExit}{southExit}{eastExit}{westExit}"
                : string.Empty;

            string separator = new string('-', location.Name.Length);

            narration =
                $"{location.Name}{Environment.NewLine}" +
                $"{separator}{Environment.NewLine}" +
                $"{location.Description}{Environment.NewLine}" +
                $"{separator}" +
                $"{allExits}";
        }

        return narration;
    }

    public static void Main(string[] args)
    {
        var kitchen = new Version02_MutableLocation();
        kitchen.Name = "Kitchen";
        kitchen.Description = "You are in a messy kitchen.";

        var library = new Version02_MutableLocation();
        kitchen.Name = "Library";
        kitchen.Description = "You are in the library.";

        var office = new Version02_MutableLocation();
        office.Name = "Office";
        office.Description = "You are in the office. There's a computer on the desk.";

        kitchen.North = library;
        library.South = kitchen;
        library.North = office;
        office.South = library;

        Console.WriteLine($"{Version02_MutableLocation.Narrate(kitchen)}");
        Console.WriteLine($"{Version02_MutableLocation.Narrate(library)}");
        Console.WriteLine($"{Version02_MutableLocation.Narrate(office)}");
    }
}