1981 fantasy fiction by
Roger Zelazny, sequel to
Dilvish, The Damned.
Following the events of the previous book, Dilvish and his demon-horse Black make their way to
Castle Timeless, home of the
mad Old God,
Tualua. The power of Dilvish's nemesis,
Jelerak, was severely attenuated at the Tower of Ice, and he will doubtless
tap his minion Tualua for a
power-up. Tualua's madness, and its influence over the Castle's environs, makes the approach to the Castle an adventure in itself - hence the title. Interwoven sub-plots and clever twists abound. See the writeup on
Dilvish, The Damned for theme, style, and RPG adaptability commentary.
There's an interesting reference near the end, regarding the Hounds of Thandolos. Sounds an awful lot like
Frank Belknap Long's
Hounds of Tindalos, right down to the time-travel context, and the depiction of the tentacular Tualua further attests to Zelazny's use of
Cthulhu Mythos elements.