From The Heretic Knowledge Vault
In context, the magical effect used by the Senilis-possessed Meji Hinadori to speed the Tsuirakuan airship fleet's passage to Praenubilus Astu, so they won't miss the festivities near the end of Errant Story. She calls it into being here, and the Akizuki Maru and her sister ship, the Ikazuchi Maru, promptly vanish into it with a poit (nice shoutout to certain other webcomics there). The other end of the wormhole is in the skies above the underground city, although access is blocked at first by a barrier erected by the insane Ian Samael, which is kind of the point.
Note that the existence of wormholes in the Real World has been postulated, invoking all manner of weird quantum mechanics and cosmology, but never actually proven. This may be one of those cases where life might imitate art, but we're not sure yet.