Ive had this idea kicking around for over a decade to make ceramic or granite slabs of sufficient dimensions as demonstrated by artifacts found from archeological digs so as to withstand elements and time and etch the surfaces of sufficient depth so as to maintain their features and then have an analog projection apparatus that uses sunlight so as to magnify the feature, also constructed of similar means. Design the components all open source buy plots in cemeteries around the world and any where else that wont be subducted via techtonics in any time soon and just bury wikipedia or whatever else. The Long now meets that scene in the time machine basically. All in the hopes of confronting this exact scenario you’ve outlined.