Watcher Beacon

The Watcher Beacons are a series of items that provide directions to the Universal Library of the Watchers.

History
The Watchers left behind beacons so that others could find their planet and, likely, bring new knowledge. After Uatu turned his people into Virals he used the beacons to lure people there so they would continue brining new knowledge.

Mentor and Drax sought a beacon but Nebula stole it from them. She used it to find the Library while Mentor and Drax had Silver Surfer follow.