These Fractal Tray puzzles are based upon space filling fractal curves and can be pretty tricky to solve. The pattern is a single line that crosses all of two dimensional spacewithout ever repeating. These puzzles follow these rules to break the line into multiple pieces that are almost identical but actually unique. Once you've taken all the pieces out getting them back into the tray is no easy task. Hilbert Curve - first described by the German mathematician David Hilbert in 1891. A square space filling pattern drawn to it's 6th iteration. This is the easiest of the three puzzles. This puzzle has 25 unique pieces Jigsaw Challenge: Challenge your mind while having fun with our mind-bending wooden puzzles. Enter an advanced realm of fitting together interconnected shapes. These geometric jigsaw puzzles will stimulate your brain. Insanely Tricky But Fun: These devilishly tricky puzzles are difficult but a blast to solve. Not only do they help relieve stress, but they can also help you relax and are a great way to connect with family. Unique Wooden Puzzle: The wooden puzzles are precision-cut from a smooth brown veneer. Each puzzle measures 13.7 × 12 cm and is 1/2 inch thick. The back of each piece is stained a rich ebony color to identify the correct side. Material: Wood Perfect for All Ages: Whether you're a seasoned puzzler or just starting, our puzzles offer challenges for all skill levels.