I grew up playing with Legos, but never constructed anything like this! Andrew Carol built a replica of the The Antikythera Mechanism, the oldest known scientific computer, which was built in Greece probably around 100 BCE. No one in the current age knew about it until it was recovered from a shipwreck in 1901. Even then, it took a century until anyone could figure out what it was: an astronomical clock that determines the positions of celestial bodies with extraordinary precision. It is an analog computer with over 100 gears and 7 differential gearboxes, and is accurate to a day or two over its range.
Now rebuilt in Lego, the video provides insight into how it works. According to Carol’s website, five turns of the central yellow handle advances the machine one year. The dials on the left represent the Saros cycle of lunar months. The dials on the right represent the positions of the sun and moon against the zodiac.