Calendar.cs

public class Calendar : Story
{
    private Region _region;
    private readonly ISet<Event> _events;

    public Calendar(Guid id, Region region)
    {
        Id = id;
        
        _region = region;
        _events = new HashSet<Event>();
    }

    public Event Schedule(User contributor, EventDetail detail)
    {
        var @event = EventFactory.Create(this, contributor, detail);

        _events.Add(@event);

        return @event;
   }
}

Region.cs

public class Region : AggregateBase
{
    private string _name;
    private Boundary _boundary;

    public Region(Guid id, string name, Boundary boundary)
    {
        Id = id;

        _name = name;
        _boundary = boundary;
    }
}