New main objective: Get the Augur's approval
Note! his quest is optional and you will get the chance to approach it no sooner than after raising Restoration to at least 90 points.
In order to activate this quest, find Colette Marence and ask her if she can teach you anything more about Restoration magic (screen above). Note - If you don't see this option, it might be a bug and in this case you will have to raise Restoration to 100 points. Colette will tell you to meet the Augur of Dunlain who you probably remember from the Good Intentions main quest. The woman will also tell you that Augur will raise your knowledge only if you get his approval first.
Exact instruction how to reach the Augur of Dunlain can be found in the description of the Good Intentions College main quest. As a reminder, you need to use a hatch (e.g. the one on the main square of the College) to reach the Midden and afterwards get to the door leading to the Midden Dark. Go across the ice bridge and choose the left corridor after reaching the fork (screen above).
Approach the Augur of Dunlain and speak to it (screen above). The magical creature will agree to share its wisdom with you, but only if you complete its trial. Before agreeing, make sure you have a party member and change the active spells to one or two of the Restoration type.
Only after getting properly prepared, accept to undergo the trial and enter the portal (screen above).
A quite untypical stage awaits you. The Augur will make it impossible for you to use any equipment and additionally take away all your spells except for those of the Restoration type. As a result, you will have to limit to defensive. I'd suggest alternating between healing and casting spells protecting you from the enemies' attacks (screen above). Also make sure not to use up your MP too often, as you won't be able to regenerate it with potions.
During this battle you will however be able to trick the Augur a bit, as he didn't forbid your party member from following you. As a result he should fight the enemies, drawing away the attention of at least some of them.
Regardless of whether you used your party member's help or not, you will have to defend for less than a minute, until you get informed of passing the trial (screen above). The Augur will reward you with the powerful spell Bane of the Undead. I'd additionally suggest returning to Colette, as you will be able to buy a new precious book from her, namely the Spell Book: Guardian Circle. Note - Before heading out, don't forget to put back on your equipment, as the game won't automatically do it for you!