I was reading about the 10,000 Year Clock, which is an interesting and romantic idea.  But I can imagine a lot of things that could go wrong in 10,000 years, mostly involving changes in culture. The clock could be looted like the tombs of ancient Egypt, it could be take by a wealthy art collector like the Elgin Marbles, destroyed by religious fanatics like the Buddhist statues of Afghanistan, or dismantled and put on display in a museum by future people who don’t share or understand the philosophy of the project.

Geodetic Satellite

If I was going to build a long-lived machine, I would do something that specifically addresses the danger of future cultural failure.  Build a dense satellite, a sphere of tungsten perhaps, and put it into a 6000 km orbit, like a geodetic satellite that will stay in orbit for millions of years.  In the surface, embed solar batteries with thick quartz micrometeorite shields.  In the core, put robust solid state electronics that transmits a repeating radio signal containing a key scientific knowledge, like a summation of Feynman Lectures in Physics, text and diagrams preserving foundational ideas like the theory of atoms, mechanics, biological evolution, and so on.

This would act as a beacon and a guardian of scientific knowledge that could survive global disasters, both natural and man-made — a meteor strike that devastates our population, or a purge of science by some future religious or eco-political movement.  None of them could stop people from eventually finding a beacon in the sky that puts them back on the road to truth, progress and enlightenment.