In the desert southwest of the US, there are thousands of Anasazi sites that haven't been excavated. Archaeologists have intentionally left them alone so that future scientists may be able to open fresh sites using new techniques and equipment. The problem is that these places become susceptible to pot hunters because they usually aren't protected. Once they've desecrated a site, it becomes worthless to science.

I recall there is a known "tomb" of a ceremonial ship next to the great pyramids. They started displaying its twin back in '82 (amazing exhibit [1]), but have left the other in place.

I also suspect that the Egyptians have a stash of known tombs that they periodically "discover" in order to keep their tourism market in the news

[1] https://en.wikipedia.org/wiki/Khufu_ship

I believe it is so, at least here in Denmark where any new hole in the ground is potentially an uncovered settlement.

I recently had a chance to visit the dig at “Ringborgen” near Køge. They only dug as little as possible and with a very directed effort: answering questions such as “what is the age”, “did they have fireplaces”, “are the signs of buildings” etc. once they got the “data” they cover the site again and preserve until new questions need answers (which potentially involves new methods).

In this case they had learned that the found settlement in Køge was build and deserted in a quite short time span. This raised a question with regards to other possible sites in Denmark: are there other sites with this pattern of it being deserted quickly? So old sites might now be redug.

Sources: had an excellent tour at the site in Køge; a friend who works as archaeologist.

The inner part of the Mausoleum of the First Qin Emperor, said to contain rivers of mercury depicting the rivers of China, etc., is still unopened: https://www.wikiwand.com/en/Mausoleum_of_the_First_Qin_Emper...

Usually, but sometimes they're going to decay anyway because of shifting groundwater. C.f. this video as an example:

https://www.youtube.com/watch?v=BAqPZ3NqVFk