Some Dragaerans, including many of the e'Drien line, levitated their castles so they were more defensible and prestigious. All of the floating castles throughout Dragaera were destroyed by Adron's Disaster when the sorcerous spells holding them up failed promptly with the disappearance of the Orb.
One of these destroyed castles in the county of Southmoor was rebuilt under the name of Castle Black and re-levitated by Tazendra and a Circle of Witches for Morrolan e'Drien in the first few years after the end of the Interregnum. Because it's levitated by Witchcraft instead of Sorcery, it should survive any future disappearance of the Orb. But it requires constant attention by a largish Circle of Witches who can't do much else in the meantime.