Soul Catcher

This door is protected by a magical seal. Or rather, multiple seals connected to the souls of the ghosts that dwelled here. You can see the remains of those unfortunate people everywhere - marauders that must have tried to solve that ghost's riddle and break into the storage. Naive amateurs!
But we won't repeat their mistakes. Look there - see that book near the far wall? I took a look when you weren't around. It's the Book of Souls that contains the names of all fallen defenders of the tower and Veligrad. When the bloody ghost seized the tower, he twisted the book's purpose and turned it into an artifact that can catch and hold souls. He used it to summon everyone who had ever lived in Veligrad to serve him. And he used their souls to seal the door to the storage.
But now we'll use the book to free the souls from this dark service and open the door. I'll tell you what to do. Use the book to capture the souls bound to the seal. It's not hard, you'll figure it out.
Just be careful! If you touch a wrong soul, I'll be in trouble.
Try not to get me killed, alright?

It worked!
I feel sorry for the souls that were used to create this seal... I hope they can rest in peace now.