Figuring out where to put all 81 numbers in one of those Sudoku puzzles so that no row or column has any number more than once? No problem. Figuring out how to use 81 nixie tubes for same? No clue!
The board, built by tinkerer John Sarik, has two knobs for selecting the correct square and a keypad for punching in numbers.
And while we're at it - things harder than making a nixie tube Sudoku board? The card game bridge. But if somehow you do know how to play bridge and are up for the (lesser) challenge, Sarik as the full schematics for the build on his site. [TrashBear Labs via HackaDay via Make]