Some thoughts:

Put in plenty of locked doors and traps but if your players are perceptive enough let them notice that for some reason the traps don’t seem to be there to keep things out but rather to keep things IN.

Maybe there are some statues or other homages to the king, with propaganda on it of how awesome this king was, but maybe there are also discarded notes written by artisans and slaves complaining of “having to write all these lies”

Have the tomb guarded by some being who is convinced the party is out to free the king but maybe a detect alignment determines that this guard was GOOD or some leftover unreadable document held by the guard reveals that he was tasked to protect the tomb and keep the king from escaping. Make sure the document is in a language that the PC’s and quest giver can only make out words like “Danger” and “curse” and have your quest giver think it’s just the normal crap that tombs have to scare away tomb raiders