I have written several times over the past couple of years about the Antikythera Mechanism, a complex astral computer built two thousand years ago. The Antikythera Mechanism has fascinated and perplexed scientists since being discovered in a shipwreck off the tiny Greek island of Antikythera a century ago (and hence the name). The Mechanism simply shouldn't exist given the modern assumptions on what the Greeks knew at the time about gearing and machines. Yet, there it is - a perfect mechanism.
As if one of machine wasn't challenge enough, Mr. Carol also built a Lego version of the Babbage Difference Engine. If you are so inclined, you can read the technical details of how each of these Lego machines was built. Personally, I don't need to make one of these machines to admire Mr. Carol's creativity and skill. And where would this world be without Legos? Who knows what might have been invented earlier if those ubiquitous little blocks had been around?