Open all Death Tombs
There are a total of 4 death tombs you must open. They are like treasure rooms and give you gear and special items. They are big doors with a dragon statue above them and have colored gems on the door. In order to open them, you have to collect 10 Book of the Dead Pages to create a chapter and sell it to Vulgrim who in return gives you a key. The 4 keys require a total of all 40 pages.
Location 1: The Nook
Fast Travel to Lost Temple entrance. You then must head South to find the door.
Location 2: Lair of the Deposed King.
This is at the very bottom of the Lair of the Deposed King. When you enter, keep going down the stairs until you reach the very bottom door.
Location 3: Lostlight
This is near the Vulgrim shop. As you travel forward you will see this door on your left.
Location 4: Shadow's Edge
When you get here, traveling towards Black Stone you will see this door to your right.
To find all the pages, follow this walkthrough HERE.