I'm always suspicious of things "planned to survive thousands of years". I'll bet politicians in Rome and Sparta big-noted themselves with "projects which'll last thousands of years!" (which they then contracted out to their brother-in-law). So far as I can tell there's not much other than Pyramids which humanity has designed/built that could plausibly claim to have "survived thousands of years", and even those didn't come close to being impregnable enough to be considered "safe" for keeping curious humans away from long half life radioactive trash...

The Romans probably aren't the best example to use to make your point considering how many structures they've built that are still standing.

Though compare the numbers standing to the many, many more which have fallen.

By "still standing" do you include ruins where, say, only part of a wall remains?

There are Roman structures that remained intact for millennia. I think the main threat to them was people re-using the masonry.

https://en.wikipedia.org/wiki/Pont_du_Gard

Agreed. And Hammam Essalihine/Aquae Flavianae is a Roman bath which is still in use.

Regarding the Pont du Gard, it's intact "due to the importance of its secondary function, as a toll bridge. For centuries the local lords and bishops were responsible for its upkeep, in exchange for the right to levy tolls on travellers using it to cross the river."

I believe bigiain's point is that the structures needed active upkeep to last thousands of years.

Your point is true about people robbing the masonry, but that's closely related to bigiain's comment about "keeping curious humans away from long half life radioactive trash".

So one solution for active upkeep, is to build radioactive waste repositories into toll bridges...

LOL! Yes, that could work. The tricky part would be to keep it from being blown up during some battle, like the Mostar Bridge.

These things are going to be buried very very deeply in a particular way. I think people would need to be a lot more than just curious.

I should add that I believe the plan is to do significant work in sealing compartments so anyone looking to wreak havoc would need to breach the facility, get down a significant distance and then work through a huge amount of concrete or clay or whatever it would be.

I think the supply line from port to the facility would be a softer target and is something the jury and stakeholders would be considering in serious detail.