The Beinecke Rare Book and Manuscript Library of Yale University, like other world-class rare book libraries, has treasures that could sell for vast amounts of money if auctioned. But it also has an item that does not have to be sold to collect cash value.
In 1624, the Dutch city of Utrecht needed to raise cash to build a dike, so it sold bonds. These are perpetual bonds--ones that never mature. The owners can collect interest indefinitely. It's also a bearer bond, so whoever possesses it can claim the interest.
In 2003, NPR reported that Yale acquired such a bond dating to 1648 from the Utrecht water authority. Geert Rouwenorst, a finance professor at the university, took the bond to the Netherlands and collected 26 years of back interest. When the library curator went to the Netherlands in 2015 to collect the next payment, it amounted to the equivalent of $153 USD.