Underground works like subways require constant maintenance just to keep from flooding and filling up with sediment; there are full time crews that work on the London Tube and New York City Subway systems that do nothing but try to prevent flooding and clean out the system. One of the effects of sea level rise will likely be the abandonment of the subway system under Manhattan Island, parts of which are already below the water table. And the weight of the city above it slowly collapsing as streets cave into the steam tunnels below and buildings fall will serve to compress the tunnels. I’d wager that the system wouldn’t even be accessible at the lower levels within a few decades of neglect, and completely filled or collapsed inside of a century.
Residues of human industrial activity may survive for millions of years; ceramics are essentially fossil-like in composition, so as long as they are buried and not under enormous shearing forces they will survive. The same is true for non-corrosive materials like gold or platinum, and of course high level radioactive waste will be identifiable as from a non-natural origin. However, pretty much any surface structure—even the Giza Pyramids or Angkorian temples—is going to be subject to weathering from sun and rain, the erosive effects of glaciation, and thermal cycling resulting in internal stresses. Structural metals—even the ‘stainless’ steels—will be subject to corrosion, oxidation, and pitting. Although Mt. Rushmore and other exposed earthworks are often cited as being impervious to aging, over geological periods they will break down due to atmospheric and seismological processes. Plastic residues in landfills will turn into an amalgam of complex hydrocarbons as it is compressed by glaciation and deposition, potentially providing a source of rich hydrocarbons and natural gas for future civilizations, but anything based on cellulose or other natural fibers will be broken down into soil.
In space satellites and spacecraft will degrade due to solar and charged particle radiation as well as erosion by interstellar “dust” (mostly ionized particles) over millions of years, and satellites in Low Earth and lower Medium Earth orbit will eventually degrade or break up due to impacts with debris, but the structure of most of the big telecom birds in higher orbits will survive even though the solar panels will be long degraded past any usefulness and the electronics will be completely fried by charged particles. The Pioneer, Voyager, and New Horizons probes will continue on their way, nonfunctional due to the decay of their radioisotope themoelectric generators (RTG) but will otherwise be basically intact. The Apollo, Ranger, Luna, and other spacecraft and components on the Moon will remain in place covered by a slight dusting of regolith deposited by the tenuous ‘atmosphere’ and the occasional meteorite impact, and even the Viking, Pathfinder, MSL, and other probes and landers will remain although significantly eroded by the thin but regular dust storms.
That our most enduring legacy might well be the wastes of once-through nuclear fission power production should be sobering to anyone who considers the significance of human civilization in context.