A little while back two NASA scientists published a paper on how you would detect the existence of a previous advanced society on Earth. Apparently, over a long time scale it's actually fairly difficult.
Now imagine detecting one, when the entire planet is covered in a 90 bar atmosphere with sulphuric acid clouds.
I'll update my downer Sci-fi novel premise. Humanity makes its first Alcubierre drive warp ship. On its test run, something goes wrong, and the ship is shifted by a vast amount in time-space. The ship arrives at an unfamiliar, abandoned star system, with a different sized Sun, vast amounts of orbital construction, but an eerily similar though slightly different configuration of planets. Over time, the test pilot crew realizes that they were merely in stasis and "arrived" back in the Solar System far in the future, and that the 2nd Venus-like planet is actually the Earth.