Calling all problem-solvers and puzzle masters: A library in Bloomington, Indiana, is home to the world's only public display of mechanical puzzles. The Jerry Slocum Mechanical Puzzle Collection can be found at Indiana University’s Lilly Library, which also houses rare books and manuscripts, including Queen Elizabeth I's Great Seal and an early printed copy of "The Star Spangled Banner."

The collection is named after Jerry Slocum, a Chicago-area native who started donating his personal collection of puzzles to the library in 2006. The library now has over 34,000 mechanical puzzles, which, unlike jigsaw and crossword puzzles, tend to feature interconnected pieces that must be physically manipulated in order to solve the problem. There are exceptions, though. One subset of mechanical puzzle called an “impossible puzzle” requires no movement at all; instead, the player must figure out how the puzzle was built.

An online database of the collection lets users search by the puzzle’s date of creation, designer, maker, or classification. The oldest item is a 15th-century Khmer iron lock from Cambodia that contains trick locks and keys. But according to Indiana State Library, puzzles weren’t always created for their entertainment value. In the second century BCE, for example, Romano-Celtic puzzle padlocks were used strictly for security purposes. It wasn’t until the 19th century that the puzzle emerged as a fun pastime.

In a YouTube video uploaded by the Indiana Daily Student, the collection’s curator, Andrew Rhoda, tries his hand at the “Gear Cube Extreme,” which looks like a Rubik’s Cube on steroids. “The puzzle is complicated by the addition of gears that move at half-turns while the rest of the puzzle moves at quarter-turns,” Rhoda says in the video.

Unless a particular piece is being conserved, visitors are encouraged to grab a puzzle and start playing inside the library’s reading room. “Mechanical puzzles are really hard to understand if you see them behind glass,” Rhoda told the student news outlet in 2017. “You can sort of understand what is going on with a mechanical puzzle if you look at it behind glass and read an exhibit label. But to really understand the idea behind a puzzle, you have to handle it. You have to play with it. You have to try to solve it.”