Shrine of Futile Truths

There's a giant gazer in the middle. To deal with it, you simply have to keep attacking and destroying its tentacles. It's other attacks are predictable and can be endured. As long as you have a great variety and plenty of stock of curatives, you should be able to withstand its attacks.

It will occasionally fill the battlefield with miasmic gas that will continuously drain your HP a bit. It's evil gaze can also instantly blind your characters, or sometimes turn them to stone. Once it suffers heavy damage, it will start casting fell magick.

Concentrate your attacks on the four summoning tentacles to stop the casting. A glowing orb will remain after you interrupt the casting. Keep attacking this orb to release projectiles that will attack the eye itself. Keep doing this until the abomination is defeated.

This enemy will also drop an Abyssal Eye, that's required for a notice board quest. Make sure to look for it and pick it up since it will disappear quickly. The door leading to the Corridor of Emptiness will be opened.