Factual error: The picture of Eddie and Teddy on the road with dad, supposedly taken in 1906, shows a Ringling Bros and Barnum & Bailey circus poster. In 1906, the Ringling Brothers circus and the Barnum & Bailey circus were two separate circuses playing in different parts of the country. They did not combine the two shows until 1919. (00:27:00)
Factual error: At the end, when Cyndi Lauper touches the glowing pyramid, goes into a trance, and starts translating the inscription, Jeff Goldblum pulls her off and she doesn't finish it. One of the bad guys says that what Cyndi already said will be enough to help him decode the rest and that it's just a matter of "cartography" now. He should have said "cryptography" (skill of decoding secret writings) and not "cartography" (which has to do with making maps).
Factual error: The address on Claire's business card reads 514 West 43rd St. When Frank gets there, the street sign is for 3rd St./900 East block. The sign on the building reads "9th Street Temporary Shelter". Along with these discrepancies, taking into consideration that 3rd St. may be the cross street, WEST 43rd would not cross 3rd St. EAST, as they are on opposites sides of Manhattan. Even if the '4' on the sign for 43rd St. were somehow obliterated, 514 still would not be on the 900 East block. (00:53:10 - 00:54:15)
Factual error: When Judge Reinhold is in the department store playing the Space Invaders video game, and one of the men chasing the skull comes to talk to him, Judge continues to play the game, so the man stands between him and the screen in order to get his full attention. If you watch the screen, the game actually continues to play on.
Factual error: The damage done by the hobgoblin-induced fantasies is real, as seen several times in the movie. Kyle's car runs off a cliff, Nick's grenades really explode, etc. Nick is in one scene set ablaze by throwing himself on a grenade, and is completely engulfed in flames from his head to his toes. But he shows up in the last scene with nothing but a few minor burns on his forearms and a pair of crutches (that he immediately discards). His hair and eyelashes are not even singed.
Factual error: The closing credits give thanks to "FAO Schwartz", misspelling the name of the famous toy store with an extra "T".
Factual error: Aphrodite mentions Medusa as her friend at point. She was a Gorgon, a monster, killed by Perseus, not a friend to any of the Greek gods.
Suggested correction: That's just the most popular version of the ancient myth. But because the story is based on a myth, and not real events, the story can change. This would be like pointing out a factual error for a film changing the origin story of a comic book character. In the poet Ovid's (47 BC - 17 AD) telling of the story, Medusa was a beautiful young woman who later was turned into an ugly woman with snakes for hair by Athena after Poseidon's actions.