I may have the record for the most outrageous treasure. A player walked out of one of my dungeons with three gems worth one billion gold pieces each.
My memory is a bit fuzzy, this happened almost forty years ago. The adventure started with a large party. There were half-a-dozen player characters. Each player character had several henchmen and hirelings. The party fought their way through the depths of my "Big Dungeon". The henchmen and hirelings died. A group of high-level thieves ambushed the party. They took everything. The left the party naked and tied up. Eventually the party managed to free themselves. This is when they found the secret passage to the lowest level of the dungeon.
I placed the Machine of Lum the Mad on the lowest level of the dungeon. Eldritch Wizardry describes the Machine of Lum the Mad as a gigantic piece of intricate machinery. The machine has a booth large enough for four people. The machine has 70 levers and 30 dials. They affect what is in the booth.
The party had nothing. No weapons, no armor, no equipment. The party ordered remaining henchmen and hirelings into the booth. They died when the party pulled a lever. The party drug the scorched bodies out. An argument ensued over who was going into the chamber and who was going to pull the lever? The characters in the chamber received some amazing powers. But, greed took over. The party pulled more levers and turned more dials. In the end, only a single player character survived. Probably the only reason that character survived is there was no one left to activate the machine.
The single, naked thief wandered through the gigantic machine. He found the Corridor of Lights that powered the machine. Gems covered the walls of the Corridor of Lights. The farther you go down the corridor the more valuable the gems become. However, you must save verses insanity every thirty feet you go down the corridor. The naked thief wandered down far enough to reach the billion gold piece gems. He extracted the gems from the wall. Amazingly, he made all his saving rolls.
Juggling the three basketball sized gems, the naked thief continued exploring the dungeon. He found a teleporter and managed to escape the dungeon with the three gems. He hid the gems while he searched for clothing and a way back to town.
The thief retrieved the gems. He tried to sell one of the gems. One gem was worth more than the entire kingdom. No one could make change for a one-billion gold piece gem. He then tried to hire a gem cutter. He found an old, highly skilled gem cutter. Upon seeing the massive gem, the cutter had a heart attack and died. The thief then found a younger, healthier gem cutter. The cutter stared into the massive gem and passed into catatonia mumbling, "The lights! The lights!"
The player realized the thief could never sell or cut the gems. He purchased a large leather bag and a mace. He placed the gems in the bag. Using the mace, he pounded the massive gems into smaller fragments he could sell.
In the end, the character had millions of gold pieces, not billions.
I found the source for the graphic here.