Ventdal is the patron demoness of those witches who seek refuge in solitude rather than fighting with other witches. The essence of that separation can be called upon to protect Ventdal's elite chosen.
Greatly increases hex resistance. Cannot be raised with training points. The only way to max Hermitage is to continually have curses cast upon oneself - a reflection of the trial of self-flagellation that Ventdal's witches went through to first earn this ability. When the trial is complete, the witch may have earned as much as 70% hex resistance.
A witch that also studies under Iwodach and has learned the Arcane Knowledge he offers (another 30% or so) can reach full immunity to Hexes.
The major exception to that immunity - enemy students of Xaerdun may have enough Curse Effectiveness to still apply curses at about 30-40%. Of course, that's still better than the 130-140% effectiveness being applied to unprotected adventurers.