Asklemmy

Hoover and three gorges dams. That much cement will be noticable for a long time.

"Low cost" levys and break waters, since those just use large cut rock dumped in the water.

A lot of modern engineering uses a more advanced type of cement than the ones ancient people used.
It's chemically stable so it doesn't react with the environment and has a predictable lifespan.
A side effect of this is that it predictably only reliably lasts about 100 years.
Older cement could react with the environment, which meant sometimes it broke really fast, but also sometimes it is able to heal small cracks and last indefinitely, if it doesn't get a mold outbreak.

The pyramids are basically a big pile of rocks, so that isn't going anywhere.

So for modern buildings, you'll want to look for structures made from cement intended to last a very long time with low maintenance near water, like the biggest dams, or things made out of cut rock, like low cost commercial port break waters.

We just don't make as many structures out of raw rock or crappy cement anymore, so it's not as likely for a lot of buildings to survive.
On the flip side, we do have a lot more buildings, so they'll probably find random elementary schools in Nevada in 4k years.