Amazon.com: BSIRI Wooden Puzzle Box Set (4 Games) - Challenging Brain Teasers 3D Puzzles for Adults, Interlocking Games for IQ Test. Ideal for Rustic Patio Decor, Unique Gift for Christmas and Birthdays :
Hardest Puzzles and Brain Teasers – Creative Escape Rooms
Calibron 12 - very difficult design from 1933 - Now with Cover
Infinite Galaxy" *Double-Side, Extra Difficult* 139 Piece Wooden Jigsaw Puzzle | Nervous System - Tri-M Specialty Products