It's rare that ruins are discovered that have immaculately preserved contents. But this is one such rare occurrence. Far beneath the surface a survey crew has used scanners to detect some constructed rather than natural hollows beneath the ground. They haven't had a chance to explore the location, but since they want the contents well preserved, they want talented individuals to go down there and look.
To begin with, the entrance to the ancient mineshaft isn't all that impressive. As with many other locations that have been discovered underground, an experience museum worker would suspect probably that the contents of the location would be degraded or subpar. After progressing some distance, though, they would find a sealed up doorway. When it is broken through?
The library is a trove of ancient and extremely well preserved books, texts of the ancient civilization that will be invaluable to the museum. One book in particular can be found inside, placed on a large obsidian pedestal. The book will open to anyone who approaches it. The text is unreadable, the language mysterious, but that doesn't seem to matter. Because if you choose a page, and wonder over that page, some item on your person will suddenly receive a unique property.
It may not be something you immediate (or ever) notice. Your pen might be excellent for killing spiders. Your pants might make you fireproof. Your jacket may slow your falls and keep you from landing so hard you would injure yourself. Whatever it is, though, you've changed something.