A divine dumping ground.

Ah, Rappan Athuk. The Haunted Halls, I have also heard it called, and I am fond of that name.
Welcome. I see you've found my journal. I have no way of predicting your principles, I have hope that this book is found by the forces of light. I will waste a little of your time with apologies: I have only recently written this record since I arrived at this place. My real journal; that is, the musings of a life lived long, full of promises and pearls of wisdom is not here. In truth, I never wrote anything down, my mind is not one to allow meaningful memories to fly to freedom. Only my impending demise has led me to pick up pen and paper, and record these words.
I will spare you stories of my life; I have had most marvelous memoirs penned before and retelling it here would probably get me in trouble with the guild of authors. Instead I will speak to you of Rappan Athuk, where I now find myself.
Rappan Athuk is a divine dump, a religious refuse, where gods have thrown everything that they don't want to deal with. "Hah" you say, so this is where old man Zelkor ended up. You're fairly funny, but that is also a bit mean. We won the war, but lost the battle. Tsar triumphs, but the Army of Light loses its way deep underground, never to return. We took the low road as it were, past their army, and nearly made it to their most unholy place. Perhaps it was a battle of greatness and glory, or perhaps we had an army of tired soldiers and wounded warriors. We lost, Leviticus won. Everything else is a detail I don't care to remember.
I attempted an express exit upon our defeat, but this place twists such spells when it wishes to. I lost General Estella near a lake of lava, and saw the last of General Agamemnon near a large cavern. I myself ended up not far from here, but I do not wish to speak of it, even if I could. When I speak of this place, it's a place where gods make pacts, agreeing to never mention what lies below. How fitting that Orcus fled here, an ammunition avalanche, the discarded weapons of those above. There is a reason his servants do not go down the well. The well is old, that's the clue. I will use the last of my magic to seal myself away as best I can. It won't be perfectly pretty nor strictly speaking sensible, but I will protect the world in the only way I can; should I die trying to flee, I would not have this key fall into the hands of anyone else. This key is strictly part of a divine off switch. Only if this world (and all who dwell upon it) are definitely destroyed should you reuite this key with its brothers. I shouldn't have to say this, but keep the key away from the demon lord, but do not take it too far from here. So long as it is within the Valley it is also protected from those who would observe it and learn its purpose.
Right. Rappan Athuk then. I have heard words and read heresay, if you'll pardon the joke. This place is very, very old, but not without some permanent residents. The goblins of Grezs' Neck live far below the surface, it is said. This is true, but it is minorly misleading; they simply live just above the Underdark, and they rarely dare to go "deeper" toward the surface, where more danger lies. They worship Snuurge, and are generally a good sort. They like to mine and sing silly songs, and pose little threat to anyone. They have numbers, true, but they know of no way to the surface, and dare not venture in Rappan Athuk proper.
There are rumors of another entrance to Rappan Athuk that lies within the forest, but stories say that it is guarded by a guardian of bone. Rappan Athuk has its own guardians, and our March of the Righteous had no quarrel with them. As we lost men, we became aware of the Black Skeletons that haunt this place. They resist a Cleric's light, as they're not animated by negative energy like their peers. Rather they are echoes of those that have died here before, taking their skill with blade and bow. They take some of the dead's rage and revenge and pour it into hunting anything living.
The great and fortunately forgotten Akbeth ended her life deep within this place, I have little interest in her for her own sake, but she was said to own a ring that defied gods. I can think of several reasons such a thing would be useful. Sadly I am unable to go and get it. If I were to try and retrieve it, I'd probably climb down a nearby cliff, brave the mazes, take the damp stairs down and look for the Mithril Gates. Or so my General tells me, being more of the scholarly sort.
The script and ink changes subtly, this was added some time after the first section.
I wish i could say more, but i am bound to secrecy. Do not grieve for old Zelkor, I lived a full life, and did something great in both life and death. Assuming I manage to be free of this place, I agreed to leave this plane and never return. Oh, but I have seen the heart of Rappan Athuk, the engine that powers this terrible place! How I wish i could tell you!
If you wonder why I know so much about this place, it is because I had the privilege of taking tea with the Architect. It is they that gave me this key and shared with me many mysteries, none of which I am permitted to record, nor name Names. What wisdom could I then Impart? There are many rumors about this place, many of them flagrantly false or just simple products of a rumor Mill. I have heard rumors myself, but believe only some of them to be true, namely those mentioned Above.
Love and Spells,
Archmage Jarrod Zelkor