The third floor of Castle Ember is taken up with a series of suites for the members of the Royal Family, prominent officials, and guests of the court. They are generally designed on the same plan : a decent bathroom, a walk-in closet, a combination lounge / study / dining area, and a bedroom. The only standard defense is locks for the doors, but accomodations can be made for more security if one doesn't want any maid service. Every suite has a series of glass windows showing the outside, letting light in during the 'daylight' hours of Amber -- ever since Queen Corrine's return to power, automated shutters have been added to the windows on the third, fourth, and fifth floors. This functionality can be overridden by the inhabitant of the suite, if desired. A "Maxwell's Invisible Air Conditioner" spell can also be activated for those who aren't adjusted to Ember's climate.
At the moment, the current Ember Royal Family is rather small -- Princess Gabrielle, Princess Keiko, and Princess Kanna -- and all three of them spend the majority of their time elsewhere, either in Amber or out in Shadow. Therefore, their rooms are not as often used as would be expected, but they are still kept in reserve for them and their immediate family members when they spend time in Ember (a new suite has been opened up for Shinobu Minor, should she desire it, and one has been in existance for Motoko for some time already).