Imagine a clock that ticks every 30 seconds and chimes once per millenium. A clock that will last 10,000 years.
The prototype of such a clock has been built. It is housed in the Science Museum in London in the Making of the Modern World exhibit.
The real clock will be much larger, large enough to walk through. It will be powered by the energy produced by the footfall of visitors and changes in ambient temperature, and it will self-correct via the sun passing overhead at noon.
The 10,000 year clock was developed in 01996 by The Long Now Foundation.