Dragon Age II -- Forbidden Knowledge -- Evil Pit

To unlock the Evil Lair and reach the Fell Grimoire, you need to destroy 5 Evil Tomes scattered around Kirkwall and the surrounding area.
-Viscount Keep's Throne Room.
-Upstairs at the south-end of the Chantry.
-Dank Cave in the North-Central portion of the Wounded Coast.
-Recently Opened Passage which is west of the Dalish Camp at Sundermount
-Cave at the East-end of the Bone Pit.

When the final book is destroyed, you are able to enter the Evil Pit at Darktown. Before heading in, consider bring a Rogue with 40 Cunning to deal with traps and also consider getting some Spirit Warding runes so you'll have a showdown against demons.
0:08 -- Evil Pit
2:36 -- Fell Grimoire
You can either read or destroy this book, but either choice results in a boss-rank Desire Demon and her entourage attacking. To avoid being surrounded, flee the room and/or summon your dog. Try to kill the Abominations and Shades quickly since they're the most likely to knockout party members. When all the demons are dead, you can loot Xebenkeck's remains for a staff that fortifies Blood Magic, (which is good to equip on Merril). Also, some treasure will spawn in the final room. Congrats! You've killed a Forbidden One demon.

[aleksattebery]

I have destroyed all the books and this option isn't available to me to find the lair. Any tips?!