It has been several thousand years since an apocalypse happened. The cause was some kind of explosion, be it nukes or a extinction-event meteor. Humans have persisted, as they do, and have effectively reverted back to the pre-medieval era. I'm wondering what human-made monuments would still be standing in several thousand years that I could add or hint at. I've already been told that something like Mount Rushmore in South Dakota will be standing for a long time, but what other things could survive an apocalyptic scenario like that?
Major Pyramids and Ziggurats
Not just the Giza Pyramids, mentioned by Patricia Shanahan, but also the biggest of the Mesoamerican pyramids, like the Great Pyramid of Cholula, the biggest known pyramid in the world, The La Danta end El Tigre pyramids in El Mirador, and the Pyramid of the Sun in Tetihuacan, all of which are already around 2,000 years old. Also the Middle Eastern Ziggurats, like the Sialk ziggurat, which dates from ca. 3000 BCE and hence is already 5,000 years old, and the Chogha Zanbil ziggurat, which is about 3,000 years old and remains about 25 m tall.
Newgrange and Stonehenge
Newgrange is an artificial hill and passage tomb dating from ca. 3200 BCE. Some reconstruction has been done on the entrance facade, but the hill itself has lasted 5,200 years.
The well-known Stonehenge monument has been standing since ca. 3100 BC. Quite a lot of it was still standing 5,000 years later when restoration begun around 1900.
Stone Castles and Temples
Stone last a long time, and so will stone castles and temples, unless they are torn down for building material (which sadly happens to many). Mehrangarh Fort in India has walls 36m tall and 21m wide, and parts of Windsor Castle are also quite solid, to name a few. The Parthenon temple on Acropolis survived largely unscathed from its completion in 432 BCE until an Ottoman ammunition dump inside the building was ignited by Venetian bombardment in 1687.
Major Modern Constructions
Mount Rushmore and Hoover Dam have already been mentioned. Also worth mentioning is the world's tallest statue, the Statue of Unity in India, which is 182m tall. There are also a number of colossal Buddha statues, of which the most famous is the Spring Temple Buddha in China at 153m. For comparison, the faces of Mount Rushmore are only 18m tall and the Staue of Liberty 46m. Even if these statues fall, their remains will still be identifiable for millennia.
The canals of Suez and Panama are also major construction feats, but they may erode and become covered in silt or mud and not be very noticable millennia from now.
Skyscrapers like Burj Khalifa (830m) are vulnerable because they are hollow, but some remains are likely to be recognizable for millennia. Under construction is the Abraj Kudai hotel in Mecca, which will become a ring of twelve 45-story towers.