https://en.wikipedia.org/wiki/Cain%27s_Jawbone
87 years after publishing it was only solved by 4 people. It took many months of the brightest minds to solve. Albeit more people have solved it since it was republished in 2022.
The puzzle is simply an unordered 100 page book, that needs to be reordered into a single continuous story which describes 6 murders. Even working out how to join a few of the pages together is a an impressive achievement for any human or AI model.
Not only does the puzzle require fiendish puzzle solving skills - it also relies on references and language from the early 20th century that very few people alive today would comprehend.
This puzzle has been my test for new models as they are released; fable still struggled to solve it - without a lot of steering over many days.
Astra just solved it from a simple “here’s the text go solve it prompt”, in under an hour, with meticulous details of individual characters and murders in check.
However it did partially cheat - there are some spoilers online which it did admit to ingesting. But none were sufficient to solve the entire puzzle.