Casting this spell on a castle or other building gives the structure the ability to fly, controlled by the caster's mental command. Although relatively slow (movement rate 3) and clumsy (maneuverability class E), the skycastle has a tremendous carrying capacity and can travel even when the caster is asleep, as it can maintain a particular course and speed unattended. Siege engines and the like affect the skycastle normally, but do not negate the dweomer until the skycastle has been breached on all four sides. A successful dispel magic removes the spell, however. In both cases, the dweomer is so large and diffuse that it does not end immediately. When negated, the spell takes time to drain, according to the following schedule:
on round 1 the skycastle stops in mid-flight; on rounds 2-5 it sinks earthward at 10 feet per round; rounds 6-9 it drops earthward at 100 feet per round; and from round 10 on it plummets earthward. Plummeting more than 200 feet destroys the skycastle and kills everyone within. If in doubt, assess falling damage against the inhabitants normally, with saving throws vs. death magic for those in danger of death from massive damage, as per the DMG.
Deliberately dropping the skycastle on a soft target such as a cottage or a living creature crushes the target, with damage adjudicated by the DM. Dropping it on a hard target damages both structures equally.
To cast the spell, the wizard must have an absolutely clear mental image of the skycastle-equal to that gained by overseeing its construction or walking every inch of it for at least one month. Reading a map or blueprints is not sufficient.
The material component of this spell is a beautifully appointed couch or sofa (1,000 gp minimum), which must be occupied by the caster for the entire turn. A new couch must be purchased for each casting.
Notes: Very rare spell. (Updated from Dragon Magazine.)