The Diamond Eyes are key items acquired in Antiqua. They are ancient gemstones that contain great power in them.
The Diamond Eyes were hidden in the Great Pyramid and Hall of Collosia. The ruler of Nobilia sought the power of the eyes, and attempted to hire many mercenaries to find them, but was unsuccessful. Then the Hero arrived, and received the task as well. The Hero met with Horace Highwater, who warned him about the ruler and instructed the Hero to bring the Diamond Eyes to him to keep them safe.
After the hero retrieved the Diamond Eyes, the ruler of Nobilia disguised himself as Horace and tricked the hero into giving the Eyes to him. At Nobilia, the ruler used the Diamond Eyes to activate the ancient statue of the sacred dog in the town square, reviving it as an ancient monster, Aegis. The hero was able to destroy Aegis, fortunately.
Some time after Aegis' defeat, the strongman Tiny stole the Diamond Eyes and went to the Great Pyramid, where he took command of the Oglins that had been released on the region after the entrance to the Oglin Caves was opened. Tinker needed the Diamond Eyes as a power source for his rocket, and the hero confronted Tiny. While Tiny resisted at first, when the hero reached his lair in the pyramid, Tiny relented and gave him the Diamond Eyes.
The Diamond Eyes were subsequently used to power Tinker's rocket and send the hero to Omnitopia.