Around the middle of Ardyl, you fill find a Unicorn cruelly chained to a post, and a small fairy floating beside it. Talk to the fairy and she will tell you how this came to be, and ask if she may accompany you to save the Unicorn before the captor returns.

Now down on level 6 you will come across a small room and a gate with only a lever on the other side. However, the fairy being so small, can slip in-between the bars and pull the lever for you (just pick her up and click on the door), though there's only a few chests in that room, nothing of importance to your quest.

Continue down to level 8 and you will come across a laboratory, again with the lever on the other side of the gate. But lucky for you, the small fairy is still with you, and will fly through the gate to pull the lever. But this time instead of the fairy coming back, an Evil Druid, the same one who captured the Unicorn, attacks you. Kill him and then venture into the laboratory, and you will find out why the fairy failed to return. She was captured just after pulling the lever, however she managed to steal the key to the padlock of the chain binding the Unicorn to the post, simply return above ground and free the Unicorn, and then speak to the fairy and she will gratefully give you the Crystal of Virtue for your help.