In an excerpt in The Atlantic from his new book about puzzles, A.J. Jacobs writes about the puzzle he commissioned from Dutch puzzle creator Oskar van Deventer, a "generation puzzle" that will take him almost literally forever to solve.

And then, on a Friday morning, I woke up to an email from Oskar. He had finished making the puzzle — and it worked. He had made a 55-pin Jacobs' Ladder. Solving it would take 1.2 decillion moves

^{1}(the number 1 followed by 33 digits). Written out, that's: 1,298,074,214,633,706,907,132,624,082,305,023 moves.We'd crushed the old record by 13 orders of magnitude. Oskar did some delightfully nerdy calculations on just how long it would take to solve this puzzle. If you were to twist one peg per second, he explained, the puzzle would take about 40 septillion years. By the time you solved it, the sun would have long ago destroyed the Earth and burned out. In fact, all light in the universe would have been extinguished. Only black holes would remain. Moreover, Oskar said, if only one atom were to rub off due to friction for each move, it would erode before you could solve it.

Here's a video about the puzzle from the guy who designed and built it:

FYI: Jacobs' book, The Puzzler, includes a "a hidden, super-challenging but solvable puzzle that will earn the first reader to crack it a $10,000 prize". Good luck!

Small rounding error here...it's actually 1.3 decillion moves.↩