Thanks to Bhel-Elryss (http://www./u/1791330/) for this joke! It's great fun in particular to retell…you'll see why at the end :)
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You thought the Chamber of the Ordeal was the only uber-cool-and-mysterious chamber in the palace, right? Well, think again.
Vania was the youngest and most inquisitive child of King Jonathan and Queen Thayet. One day, while exploring one of the oldest at most undisturbed parts of the palace, she came across a large bronze door set between two marble pillars. She attempted to open it, but in vain; the doorknob would not turn. She decided to pick the lock, and then found that there was no keyhole!
Vania went off and found her parents.
"What is behind the door?" she asked.
"A great secret", replied Jonathan, "which has not been uncovered in over a thousand years."
"So how do you open the door?" she asked.
"The door opens itself", answered Thayet. "It will open only for the person who has travelled the land, and counted every blade of grass and every grain of sand within it."
Vania grew up and dedicated her life to finding the secret. Many years later she returned to the palace. In her head were images of foreign places and all the blades of grass and grains of sand that she had counted.
She walked through the great bronze door which, at her approach, had swung open soundlessly. Try as they might, no one else could cross the door's threshold. Vania walked into a grand hallway, which lead to a silver-encrusted door. This too opened. At the end of the resulting corridor was an even more elaborate door, made of gold, and decorated with emeralds and diamonds. The door opened just enough to let Vania through.
…
What? You want to know the secret? Well…you'll have to count every blade of grass first.