You can download Sudoku puzzles in the common size of 9x9 cells from this
page. The Sudokus are offered in different difficulty levels and they have
all different solutions. So if you solved the easy puzzles, you can download
the medium or difficult ones and get a complete new set of Sudokus.

The submenu on the left gives access to more pages that contain Sudoku puzzles
in other sizes.

All Sudokus that you can download from these pages have principally only one
solution. For the easy to difficult puzzles, it is also ensured that always
at least one cell with a unique solution exists. In contrast to this, you will
encounter game situations in very difficult Sudokus where no cell with a unique
solution can be found. In this case, you may need to try different
numbers in a cell to find the solution.

30 very difficult Sudoku puzzles with 9x9 cells (14
KB). (While playing these Sudokus, you will sometimes find no cell with a
unique solution, so that you may need to try different numbers for a cell
to find the puzzle's solution!)