Obtaining this book, and the 4 others, is required for the Master Quest Cape. You must read this book before you will be able to obtain the next one. You do not need to be on Slayer assignment to obtain these journals.
Below is the text you can read from within the book.
Death. Every time I cross that threshold and face the Underworld, I find myself overcome with curiosity. Each time I stand in that 'lobby' we call the Underworld, I marvel at how solid it feels. At how beneath my feet feel stone, my lungs seem to breathe air and how the cold seems to enter my bones and cause me to shiver.
Yet I know that this place is not, cannot, be real.
My thesis is that this Underworld is formed not of matter, but of the memories of matter, of the detritus left behind by the souls that have passed on, like a snake shedding its skin. This would certainly explain why the afterlife of each world seems to mirror, in some way, the people of that world. Or rather their expectations.
On my home world, the Underworld is cold and precarious - a great frozen lake leading across to a temple that may once have been a mead hall, now transformed by the beliefs of the more recent dead.
But here, the afterlife recognises the gods that both guard and devour the dead. Most intriguing.
There are times when I yearn to continue on, to shed this snakeskin life and to see what awaits my soul beyond this limited physical existence. But I cannot, I have too much work left to do.