A League airship the Mountainfolk got their hands on
When the Circle drove the demons laying siege to Diamond Hearth off, there was much appreciation. That manifested in the form of the Helsanti League gifting a broken airship to the Circle. The Mountainfolk allies of the Circle then proceeded to upgrade it, turning the Essence Cannon it had previously mounted into a means of propulsion. That allowed them to race across the sky at unheard-of speeds; covering the entirety of Creation in barely 2 weeks.
After almost a year of faithful service to the Circle, the airship holding the speed record for a circumnavigation of Creation met its end in the East. The Circle had taken her to intercept an unknown party of horsemen, which turned out to be a Circle of Deathknights. Their archer, Warden of the Darkest Path, severed the gondola from the gasbag and brought it down.
The airship, though, would not o quietly into the night. Her wreckage killed Undaunting Sabbath as it fell. That wasn’t it,though. Its Essence Drive had been damaged, and was drinking in the Essence of eleven totemic anima banners at an alarming rate. Geralt used it as a battering ram before he flung a large piece, including the drive, directly at Thorns. His throwing arm was apparently good enough for the drive to reach Thorns, and exploded in a massive blast of energy over the Deathlord stronghold.