The Eye of Stars
This device resembles a monocle on a fine silver chain. If you look through it at the sky, the stars and other heavenly bodies become clearly visible even in bright daylight and through the densest clouds.
The Eye rightly belongs to the elf prince Olimandorél, who bought it from an invisible gnome in the Luskan marketplace long ago for the sum of 5 silver pieces. It was stolen from his castle by a servant who was caught and beheaded but by then the Eye had disappeared.
There is a long-running and, at times, bitter dispute between the Guild of Astrologers and the Guild of Navigators over who owns the constellations*. If the Eye were to be offered for sale (secretly, because it is stolen property) the respective guildmasters would undoubtedly compete against each other to own it.
Next item: The ears of an unlucky rabbit
* It all started with a row about the XVIth constellation, Ancoronam, the Crown and Anchor. Navigators treat the Crown and the Anchor as two separate constellations because they lie on either side of the equator, whereas Astrologers treat them as one because otherwise there would be 17 constellations and 17 is an unlucky number on Fridays.