This is a phenomenal piece of clockwork engineering: the 10,000 Year Clock, created by (or being created by) the Long Now Foundation.
From the site:
Designed by Danny Hillis, the Clock is designed to run for ten millennia with minimal maintenance and interruption. The Clock is powered by mechanical energy harvested from sunlight as well as the people that visit it. The primary materials used in the Clock are marine grade 316 stainless steel, titanium and dry running ceramic ball bearings. The entire mechanism will be installed in an underground facility in west Texas.
In 02011, The American Astronomy Society published a paper co-written by Danny Hillis that describes how the Clock reckons time over its 10,000-year design lifetime.
For more information, check out their working prototype, or just browse the photos below: