Amazon.com: KAILIMENG 5 Linked Rings Metal Puzzle - Hard Sequential Movement Puzzle - Brain Teasers Mind Game for Adults and Kids - Classical Trick IQ Toy (Length 4.5 Inches) : Toys & Games
Recursive interlocking puzzles
C-Space Tunnel Discovery for Puzzle Path Planning
Recursive interlocking puzzles
The Puzzle That Will Outlast the World - The Atlantic