Like a huge clock in a mountain to tell the time for 10,000 years
http://www.kk.org/thetechnium/archives/2011/06/the_clock_in_th.php

Or a stone monument to tell people how to rebuild society after the apocalypse
http://www.wired.com/science/discoveries/magazine/17-05/ff_guidestones

Or a nuclear waste bunker meant to be unopened for 100,000 years
http://en.wikipedia.org/wiki/Into_Eternity_%28film%29

Is there more amazing stuff out there being built by awesome secret societies etc? Do you think there'll be much we recognise today still standing in 1000 years time, or 10,000?