Tower of Artifex
From The Heretic Knowledge Vault
The Tower of Artifex was a structure in Tsuirakushiti that was destroyed or at least damaged at some indeterminate past time, when someone crashed an airship into it. We don't know much about it, except that Tsuiraku went moderately paranoid over security as a result, and airships seem to have lost a certain amount of their attractiveness as a means of transportation. Mentioned here without much elaboration.