Pretty fascinating:

More than a hundred years ago an extraordinary mechanism was found by sponge divers at the bottom of the sea near the island of Antikythera. It astonished the whole international community of experts on the ancient world. Was it an astrolabe? Was in an orrery or an astronomical clock? Or something else? For decades, scientific investigation failed to yield much light and relied more on imagination than the facts. However research over the last half century has begun to reveal its secrets. It dates from around the 1st century B.C. and is the most sophisticated mechanism known from the ancient world. Nothing as complex is known for the next thousand years. The Antikythera Mechanism is now understood to be dedicated to astronomical phenomena and operates as a complex mechanical “computer” which tracks the cycles of the Solar System…

During October 2005, another team of specialists from the cutting-edge company, X-Tek Systems, came to Athens… Their aim was to use the very latest x-ray technology to look at the internal structure of the mechanism with its complex and confusing gear trains. With them they brought the prototype of a very powerful new x-ray machine, the eight-tonne “Bladerunner”. Originally designed to search for minute cracks in turbine blades, this machine gives astonishingly detailed three-dimensional x-rays, using the latest “microfocus” x-ray techniques. It has opened a remarkable window on microscopic internal details of inscriptions and gearing at a resolution better than a tenth of a millimeter. Inscriptions can now be read that have not been seen for more than two thousand years and this is helping to build a comprehensive picture of the functions of the Antikythera Mechanism.

More… (source)

Articles about this project published in Nature can be found here.
A reconstruction of the device can be viewed here.