The World Heritage-listed Mausoleum of the First Qin Emperor in the Shaanxi province of China was constructed in the third century BC. It is a necropolis, of which the "garrison" of Terracotta Warriors is probably the best known feature.
The Chinese history Records of the Grand Historian says the tomb chamber has arrow traps and "rivers" and "seas" of mercury. The craftsmen who worked on the mausoleum were said to have been buried alive inside of it.
Unusually high levels of mercury have been found at the site, lending credence to the account of "rivers of mercury". However, others have attributed the readings to local industrial pollution.
The risk of active traps and mercury poisoning are sometimes given as the reason why the main tomb chamber - where the first emperor of China is presumably buried - is yet to be excavated, although it seems more likely that the Chinese government is waiting until the resources and technology are available to preserve the mausoleum when it is excavated (a range of reasons are given here).
When will the the main tomb chamber of the mausoleum of Qin Shi Hua be opened?
This question will resolve positively according to credible reports that the main tomb chamber at the mausoleum complex has been opened at least enough to admit a light and a camera (i.e. a person doesn't need to gain entry provided there's enough of an opening to see inside).
This will also resolve positively if an opening is created by natural causes, retroactively if an existing entrance is found and reported after the opening of the question, and ambiguously if an existing entrance is reported to have been found before the opening of the question.