A piece of writing that has been encrypted or encoded. Typically, it is your job to decode the writing.

Included in this category are brain teasers and puzzles that are mathematical, or require the usage of logic to solve them.

Also called Paint By Numbers Puzzle, Japanese Puzzle or Gridlers. This category contains games that can be printed and played on paper, and general information sites about nonograms.

Contains sites with collections of optical illusions.

Rhyming Brain Teasers

Created as "Number Place" in the 1970s, this logic puzzle gained mass popularity in Japan in the 1980s. "Sudoku", or "Su Doku", is Japanese for "number singly." In 2005 it gained great appeal in the United Kingdom and is rapidly expanding to the rest of the Western Hemisphere. The aim of the puzzle is to place a number from 1-9 in every square in the grid so that every row, column and 3x3 "region" includes each number once only. While numbers are most often used, this is only for simplicity. No math is required, only logic. There are also variants using letters or symbols, different-sized grids, overlapping grids, and other variations.