"Pass me the blue one." said Quinn.
"Are you sure?" asked Elise. "It's just, you were sure about the last two combinations, and that ceiling got closer both times."
"It's a gamble, I agree," replied Quinn, "but whatever's behind this door has got to be worth it."
Elise passed Quinn the blue stone which he placed carefully in the final slot. As the grinding began, Quinn looked to the door while Elise looked up...
"What do you mean the vault is empty?!"
"Just that, sir. It's empty."
"There was a half tonne of gold coins in there! Did you see a cart? Any orcs or ogres? A dragon?! It's not like it just got up and walked away!"
The adventurers hear a noise and turn, only to see a bottle clatter down the street. Shrugging it off, they continue on their way, blissfully unaware of the hulking mass of junk taking shape behind them...
You find a book in the library, then when you start to read it, seems to change from pages of words to pages of images that seem to live and move. If you touch the page after the images appear, you travel into the story and now live in that world.
There is a book on that world, that leads back to this one.