So, you may have head of the Mausoleum of the First Qin Emperor. This is the one with the famous terra-cotta army (including horses and bronze chariots). The rumors of rivers of mercury as a part of a miniature model of China. And you may have heard about how the tomb remains sealed and what may lurk within. And how all of this was constructed to honor Qin Shi Huang and ensure he lived a full and rewarding afterlife.
And then people forgot were the tomb was.
So, the main thought here is how his concubines, ministers, tomb builders were all killed and buried with him. The terra-cotta army was buried to provide Qin an army in the afterlife. How all of this was meant to magnify his life and glorify his reign. He was, after all, the first person to unite what became China.
But all historical evidence tells us he was kind of an SOB.
So there's a whole AD&D adventure aspect of this place. Like the lair of the Lich King, living within his death, calling forth all the pleasures of the world, directing his terra-cotta army in new conquests and defending his final resting place.
So, let's populate something similar, but not exactly the same.
Okay, then let turns that script. This wasn't to keep people out, and protect the first emperor. This was all designed to keep the bastard in. To trap his eternal soul and deny it achieving any spiritual afterlife. Sure the term-cotta army is there and would strike any who would attempt to breach the tomb, but to keep them from releasing the emperor. What if their real mission is a last line of defense against the emperor from escaping his elaborate tomb with its myriad traps and rivers of mercury?
Or what if it isn't actually the emperor, but something else? Something the emperor sacrificed his own plans for immortality in death, something that threatened all he has accomplished. Something he barely was able to contain.