Yin & Yang by Doug Engel is an interlocking puzzle available at SeriousShops.com. It was entered at the 2004 24th IPP Design Competition, at the time by the name of Double Monad. This ancient Chinese symbol, that represents opposite interconnected forces in harmony, is an inspiration even in puzzle building, which at first glance, it doesn't remotely look like a puzzle.

Like every other puzzle like this, the goal is to take it apart. There's four interlocking nickel plated pieces that together make two overlapped Yin & Yang symbols. When you take it apart, your new and probably harder task is to return it to the original form. 

Since the pieces aren't very tight together, you'll be able to move them easily. It doesn't mean that it's that easy to solve though, because you still have to figure out how the pieces are joined together and which one will be released first. For a first timer, it may take a while to solve it, but if you're used to this type of puzzles it shouldn't take you more than 10 minutes.

The presentation of the puzzle is very pleasing, with its elegant and charming design, which was what got my attention in the first place. It's a simple, but beautiful concept and looks great on a desk...

The Yin & Yang is currently being sold in some European puzzle stores between €25 and €30 (~$32-$39 USD). That's why I was so impressed to see it at $13.95 in SeriousPuzzles.com, so get it while you can.