The University of Chicago is trying to find out who sent a mystery package apparently containing a notebook used by Indiana Jones in Raiders Of The Lost Ark.
The parcel was received by the admissions department and was addressed to Henry Walton Jones Jr.
There is no Henry Walton Jones Jr working at the US institution - but officials made the connection to Indiana Jones, as it is the fictional archaeologist and adventurer's given name.
Inside the package was an elaborate replica of a journal by his mentor, university professor Abner Ravenwood, from the movie about the Ark of the Covenant - but with no explanation.
The university said of the package's contents: "The book itself is a bit dusty, and the cover is teal fabric with a red velvet spine."
It had "weathered inserts and many postcards/pictures of (the character) Marion Ravenwood (and some cool old replica money) included".
"It's clear that it is mostly, but not completely handmade, as although the included paper is weathered all of the 'handwriting' and calligraphy lacks the telltale pressure marks of actual handwriting."
Once pictures of the package were posted on Tumblr , responses starting pouring in.
Admissions counsellor Grace Chapin said one theory was that it was an "alternate reality" game where players plant clues for others.
Another was that it could be part of an Indiana Jones promotion, but Ms Chapin said Lucasfilm, the studio behind the Indiana Jones movies, insisted it was not responsible for the package.
Ms Chapin also said she had never received any kind of mail like this before.
The Chicago Tribune News quoted her as saying: "It's been wild for us. We're going to be posting a follow-up with all the explanations we've been getting and what we know later."