Today, I saw a book called "Sudoku" in the local bookstore, proclaiming "Revolutionary worldwide hit - wordless crosswords". If something is worldwide hit, I presumed I could also find it on Internet. And I did. The idea is extremely simple. The puzzle is always a grid of 9x9 small squares (or, in other words, 3x3 big squares, each consisting of 3x3 small squares). Some of the squares have numbers in them. For example:
Your task is always the same: "Fill in the grid so that every row, every column, and every 3x3 box contains all the digits 1 through 9." That's all. This might take from 10 to 30 minutes of your time. There is always only a single solution. For the problem above, the solution is:
This reminds me a little bit of my favorite old GameBoy game "Mario's Picross", also known as CrossPix, Nonograms, Griddlers, CryptoPics and under other names.