This is probably more a twist for a fantasy adventure but could work for science fiction. The party of player characters are searching for the Tomb of Dude Rex and think they find it but it turns out to be his cenotaph. A cenotaph is an empty grave created to memorialize the dead individual and his real tomb is elsewhere. In the Old Kingdom Egypt the first dynasty rulers had a tomb and a cenotaph both; one in Upper or southern Egypt and one in Lower or Northern Egypt. This occured because the 1st dynasty rulers were the ones that unified Upper and Lower Egypt thus the ruler was represented in death in both lands. The modern controversy is which is the tomb and which is the cenotaph.
Its a twitst from the real world and cetainly one that I dont remember ever encountering in an RPG.
Another twist- the true treasure is hidden in the cenotaph but cannot be uncovered without clues from the tomb- as the dead king was worried about grave robbers. Perhaps the dead king rises as a liche and forgoes killing the player characters that disturbed his slumber being anxious about his hidden treasure back at his cenotaph.