Although some people have already revived this challenge in the recent updates(only since 1.10 though), I thought this was interesting that one of the oldest challenges in Minecraft is played by a more famous YouTuber who has already done this challenge back in 2011.

For those that don't know what the 404 challenge is: You basically have to gather resources before night fall. When night fall happens, you must head down below the depths of the earth and you MUST stay down there forever! The fastest way to get there is to dig a big gravel area where it already has a way down to the surface level with diamonds in it. You can't use torches! Anything else is allowed though. And lastly, it must be set to hardcore mode. When you die, it's over! Unless you wanna try again.
Here's a source to the original challenge forum: https://www.minecraftforum.net/forums/minecraft-java-edition/seeds/298932-ironman-challenge-series-404