The Tower of Octavius (Nov 2008) "is a complete kit for incorporating this mighty stronghold and its occupants into your GURPS fantasy campaign, including suggestions for setting it on Yrth.
Along with 10 pages of maps, the book features a detailed description of the six-level tower, plus its basement, dungeon, and crypt, and the region around the wizard's tower. It provides full GURPS information on its powerful, eccentric occupant -- Octavius of Tyrvo, the Wizard-Baron -- and his minions and allies. You'll also find plenty of ideas for how to add this ominous abode to your campaign, as a one-shot place to visit and perhaps overcome, a recurring point of interest, or the basis of an adventure series."