As institutions go, and depending on the nature of the content, I suggest considering saving it in https://FamilySearch.org , if it fits properly in a "stories" or "photos" or such concept that can be related clearly to family history.
It is sponsored by the Church of Jesus Christ of Latter-day Saints, which is almost 200 years old as an organization, which plans to last for a very long time; financially conservative (strong savings and effectively no debt), tech savvy, have strong traditions of decisions by consensus (or unanimity of leaders), and owns among other things a climate-controlled vault inside a granite mountain that has contained large amounts of microfilmed genealogical records (now digitized -- yay!). As family-oriented (ie, for preserving multigenerational culture among other things) as they come. One goal is to learn Adam's/everyone's family tree, as far as possible, and keep it forever. There are of ~ 17 million members (I am one), and for many reasons it seems likely to stick around a long time (I gather that Tolstoy also thought so, when he visited, when it was much smaller :) . (They also own Brigham Young University aka BYU, and holds a twice-yearly conference whose contents are translated to like >90 languages, I think several dozen languages live during it, and heard or read by people in some 220 countries, if my rough memory serves.)
I guess the site could have some size limit on what can be added from one person's account, or attached to one particular ancestor, or something, but the web site with all features is free, and I don't know why that would ever change. I used to work there (among many) on some back-end stuff.
(Edits to the above for clarity, working there, and the Tolstoy & BYU mentions.)
Edit: I'm curious: what is the general nature of the content you would like to save for 500 years? Sounds intriguing. Would it be useful to others also? Another idea would be to put it in wikipedia and/or archive.org, if it really doesn't fit in familysearch.org .
It is sponsored by the Church of Jesus Christ of Latter-day Saints, which is almost 200 years old as an organization, which plans to last for a very long time; financially conservative (strong savings and effectively no debt), tech savvy, have strong traditions of decisions by consensus (or unanimity of leaders), and owns among other things a climate-controlled vault inside a granite mountain that has contained large amounts of microfilmed genealogical records (now digitized -- yay!). As family-oriented (ie, for preserving multigenerational culture among other things) as they come. One goal is to learn Adam's/everyone's family tree, as far as possible, and keep it forever. There are of ~ 17 million members (I am one), and for many reasons it seems likely to stick around a long time (I gather that Tolstoy also thought so, when he visited, when it was much smaller :) . (They also own Brigham Young University aka BYU, and holds a twice-yearly conference whose contents are translated to like >90 languages, I think several dozen languages live during it, and heard or read by people in some 220 countries, if my rough memory serves.)
I guess the site could have some size limit on what can be added from one person's account, or attached to one particular ancestor, or something, but the web site with all features is free, and I don't know why that would ever change. I used to work there (among many) on some back-end stuff.
(Edits to the above for clarity, working there, and the Tolstoy & BYU mentions.)
Edit: I'm curious: what is the general nature of the content you would like to save for 500 years? Sounds intriguing. Would it be useful to others also? Another idea would be to put it in wikipedia and/or archive.org, if it really doesn't fit in familysearch.org .