In 2010 a small picture shipped with Minecraft: a mountain, a waterfall, a beach. pack.png, 128 by 128 pixels, the icon of the default texture pack. In 2020, fans found its world. Every world grows from one number, its seed, and Java's random numbers only have 48 bits inside, so in the finders' count a random seed was one of about 231 trillion (2^48 x 0.82). No one could open them all and look.

So they threw worlds away. Streaks in the water showed which way the camera faced. The clouds are the same every time the game starts and only drift one way, so they pinned the spot: the waterfall's source block at z = -31. Then the beach: where the sand and dirt lie became a test any seed can fail without ever opening the game. Minecraft@Home volunteers ran it across every seed with BOINC, the compute-sharing platform: about 700,000 were left. Then four blocks of ground, heights 77, 78, 77, 75. One seed was left: 3257840388504953787.

pack.png is Mojang's image, so it isn't shown here. The toy world, the picture and the search in this film are our own simplified version, built in code: 16,777,216 toy worlds, 216 left after our beach test, one after our ground test. The real numbers are the finders'. It all started, as the project's FAQ puts it, with a YouTube video made by SalC1.

Which clue would you have checked first?

Sources: Minecraft@Home and the pack.png project, "Pack.png seed reversal methodology" (2020); packpng.com FAQ and details (archived 2020 and 2021).
Not an official Minecraft video. Not approved by or associated with Mojang or Microsoft.