I'd like to call this item a "Scroll," but after what Bethesda said about Notch's new game, I'd rather settle on a Message.
Our kingdom's greatest warriors have fought against many evils, some have returned, other haven't. Though, they might not be the accused ones. Well, Donald the Almighty is, but that's not the point. That is a story of its own.
My liege, please listen. Every time we send our newly trained hero in the unknown darkness to vanquish evil, and they've failed, it might be not entirely a loss. It might be true that the Goblins fled with all the riches our heroes possessed*, that the Gnolls had a nice meal from the corpse of our lost fighter, and that the Naga would create a new statue for their front yard from the remaining pieces. It might even be true that the Vampires would resurrect our hero to increase their army when the Gnolls and the Vampires aren't looking.
But there's one thing that now goes lost and shouldn't go lost: knowledge.
Our Mathemagicians made some improvements with their Mathemagics. They can now inscribe a piece of Message that a wearer can possess, holding knowledge about the surroundings around him. Because of the secret language of the Message, most people can't read it. Most people would read it as just zero's and ones, but the Mathemagicians can read it fluently. The magical Message will script itself (I don't know what that means.) to write on itself what it knows, filter only the important things and teleport back to the city once it can't feel the wearer's life anymore.
I hear you think: WEYTWUT? It seems beyond magic to me, too. But the Mathemagicians are sure about their work. They can simplify our future lives, making better preparations for heroes to enter the darkness once again.
*We have some interrogations with the Goblins to regain some of our lost stuff, for the ample fee of 100 coin.
SUGGESTION: Preparation -- Memory Message: If you die while wearing this in a dungeon with a random boss, the next time, it will be the same boss.