Here are 3 treasures that you can find in the Long Halls of Luroc.
Casket of Brealough
Common Knowledge: The Casket of Brealough is full of ghosts what'll smite yer enemies.
Rare Knowledge: Pajranwald the Bashan suffered the loss of all his forces after the unsuccessful siege of the monastery of Gemba the Squeamish. After this setback, Pajranwald was forced to find a new method to challenge his rival. Towards this end, he quested for the Casket of Brealough, a goal which he ultimately attained. Upon opening the box, Gemba the Squeamish was struck with a sudden change of heart, and immediately ceased his oppression of the Bashan people, disbanded his army, and distributed most of his wealth to the poor.
DM Knowledge: The Casket of Brealough is an artifact with the power to completely rewrite your campaign. When the Casket is opened, the darkness inside seems to swallow up the whole universe. The person who opened the casket now switches roles with their worst enemy. The opener's close allies (the other PCs) are likewise switched with the nemesis' lieutenants.
The memories/intentions/personalities of the people who switched are preserved, but the rest of the world is rewritten as if it was always that way. Change as few things as possible. The character sheets, for example, should stay the same.
The villain, now that they are sitting in your shoes, will probably realize what has happened and will probably make plans to kill you and/or recapture their old position. Remember, they probably know all the secret paths into your new castle--and you probably don't.
Example: Alice has tracked down the Casket to defeat the evil necromancer Bob. Upon opening the Casket, Alice is briefly dazed, but then quickly notices that all of her companions (the other PCs) clothing has suddenly turned black, and now has a definite skull motif. Disappointingly, there is no sign of the Casket. Weird. As the PCs leave the dungeon, they notice a bunch of necromantic minions standing guard by the dungeon entrance, watching outward.
Alice draws her sword but the ghouls are like, "Mistresssss, have you found what you were looking for? Are you injured?"
Alice is like, "What."
The ghouls are like, "We must return quickly to the Black Tower before Sir Bob reaches it with his company of Mighty Heroes. They intend to crucify you, mistress!"
Alice is like, "What."
The ghouls are like, "Also we're hungry and bored. Let's go, mistress."
Sheet Music for the Empty Aria
Much like the Pamphlets of Avool, the Empty Aria is apparently a non-magical piece of paper that creates an extraordinary result. (The process by which a non-magical thing creates something magical is still not understood. It is also possible that the Empty Aria is just a subtler form of magic that only seems non-magical, or something else entirely. (The process by which a non-magical wizard memorizes a magical spell is another example of non-magical materials producing a magical result, so there is some precedent here.)
The Empty Aria is a 11-minute song written for a single singer, optionally with violin accompaniment. The song is technically demanding and crosses several octaves, so that only the best singers can perform it successfully.
When sung correctly, the singer dies halfway through the song. However, the voice does not--the song continues with the disembodied voice filling the air.
Different experiences have been reported. Some claim that the singer's voice takes on a melancholy tone, or a triumphant one. Others say that the voice becomes impossibly loud and inhumanly beautiful. And yet others say that the song differs drastically from what is written on the page.
Any listeners get +2 to save versus death effects, forever.
The accompanying violinist, if any, loses their voice but becomes forever immune to death effects. Since the violin parts of the Empty Aria are equally demanding, a talented violinist is also required.
The Metasyntactic Hammer
The Metasyntactic Hammer is difficult to describe. It is, obviously, a hammer, but it is also an undefined object. It occupies an incomplete idea-space in the universe. It's a semiotic blur. Instead of existing as an actual, physical object, it merely a set of symbols that code for a hammer. A semiotic blur.
At any given time, the metasyntactic hammer can function as either a hammer or the last tool that it was touched. If it last touched a rope, it can be used to rappel down a wall. If it last touched a knitting needle, it can be used to make a scarf.
This is not a transformation, but rather a redefining of what the object actually is. In addition to it's new, redefined uses, it can always function as a hammer.
Reality flexes to accommodate these new definitions, but in the case of clear and irreducable paradoxes, terrible things have been known to happen.