ToME: the Tales of Maj'Eyal

I am playing on v. 1.5.10B.

When I got to the end (4th level) of Old Forest there was a huge castle which I cleared and a path to the Lake of Nur however there was no sign at all of the boss which would allow me to complete the "Into The Darkness" quest. I also backtracked and looked on all of the other levels and cannot find the boss either. Does anyone know where I can find this boss so I can complete the quest? Thanks.

You may need to look a little harder as not all bosses will run at you. If you had the version of Old Forest with crystals, that boss will try to run away from you at times. Try running around the last floor with Track or a similar item/talent. If that doesn't work, well... perhaps it's behind a tree that you need to dig through?

I don't know what to tell you if it's still not around.

If the Troll Castle spawned in Old Forest 4, then the boss is probably not there.

Completing the quest is meaningless, so don't worry about it.

A little off topic, but interestingly the backup guardian for Old Forest is often missing as well for no apparent reason.

There is a mod for missing bosses, and a method for resetting zones.