Ok so this is a bit of a story one, so it's a bit longer. I can't remember who came up with this joke though

One evening a man is driving his car down a winding country road but it breaks down just outside a monastery. He knocks on the door to ask the monks for help and they do. They feed him, let him stay the night, and even fix his car for him. In the middle of the night he hears a weird indescribable sound. The next morning he asks about the sound to the monks, but they reply saying "sorry, we can't tell you because you're not a monk", and soon after that he leaves and gets on with his life.

A few years later, he's driving down that and country road and his car breaks down in front of that same monastery, so once again he knocks on the door asking for help, and once again they feed him, let him stay the night and fix his car. Once again that night he hears the same strange noise that he heard years ago, and once again when he asks about it in the morning they say "sorry, we can't tell you because you're not a monk". The man is desperate to know what the sound is, so he asks "how do I become a monk?". They say "to become a monk you must travel the earth and count the number of grass blades and pebbles" so the man leaves to start his difficult quest.

The man comes back 58 years later, knocking at the door. He tells them "I have done what you have asked. I have counted the number of pebbles and the blades of grass throughout the earth. There are 4667536734677 blades of grass and 4574568666 pebbles. Can I please know what that sound is now?"
The monks reply saying "you are now a monk. We shall show you where the noise is" and lead him outside into their back garden.

When they get out, the man sees a large wooden building. He goes to open up the wooden door, but it is locked. He asks for the key and they hand it over.

He is greeted with another wall and door, this time though made of stone. When they go through there is another wall and door, made of iron.

Inside each door is another door, made of a different material. Gold. Rubies. Sapphires. Amethysts. Topaz. Rose Quartz.

And then, finally at the door made from diamond do the monks hesitate before handing him the key. Before they hand it over they say "this is the last door. Beware what you're about to see is life changing, and you won't be able to look at reality the same way again".

The man nods as he takes the key from them and unlocks the door, gazing at the source of the sound with surprise and enthusiasm. He would tell you what he saw that day, but he can't because you're not a monk.

:3