Suguru, also known as Tectonics or Number Blocks were invented in Japan by Naoki Inaba, a very prolific puzzle designer. These puzzles have very simple instructions, but a very wide spectrum of difficulties, ranging from easy to insanely challenging.

Suguru puzzles are quite different than Sudoku, so you'll want to read these rules carefully:

You'll see that the grid is subdivided into containers or cages, each of which is 1 to 5 cells in size. You need to fill each container with unique digits, counting up from 1. So for example a 2-square container contains the numbers 1 and 2. A 5-square container contains the numbers from 1 to 5. Adjacent cells may never contain the same number, and this includes diagonally adjacent cells.