The Antikythera Mechanism is the oldest known scientific computer, built in Greece at around 100 BCE.
Lost for 2000 years, it was recovered from a shipwreck in 1901. But not until a century later was its purpose understood: an astronomical clock that determines the positions of celestial bodies with extraordinary precision.
In 2010, this fully-functional replica was built out of Lego by an Apple Engineer.
Read more about it here.