Good point! The longest-lived artifacts would probably have to be somewhere with much less weather and geological activity than the surface of the earth. Maybe if you put a structure in orbit or perhaps on the moon?

Paradoxically, extending on your thought - I guess anywhere with living conditions similar to earth (oxygen atmosphere, water, weather, etc) would not be conducive to long term archival of civilization artifacts.

So you'd have to look at 'dead' places if you want to find evidence of civilization. Or stumble across an derelict megastructure (dyson sphere\niven ring\etc)