Danish inventor Jens Olsen spent 27 years building the World Clock in Copenhagen. It began keeping time in 1955 and will supposedly be able to accurately keep time for the next 570,000 years.

The clock consists of 12 movements which together have 15,448 parts. The clock is mechanical and must be wound once a week. Displays include lunar and solar eclipses, positions of the stellar bodies, and a perpetual calendar, in addition to the time. The fastest gear completes a revolution every ten seconds and the slowest every 25,753 years.

Source: https://en.wikipedia.org/wiki/Jens_Olsen%27s_World_Clock, https://www.factretriever.com/denmark-facts