The Voyages of the Argo quest is a sub-quest for the Voice of the Night Sky storyline (concerning the Constellation Coins). In your notebook, the description reads:
An ancient painting of the Argo and the Argonauts, by Lorenzo Costa, painted around 1500 A.D.
"The Argo was a ship in Greek mythology that Jason and the Argonauts sailed on to get the Golden Fleece from Aries the ram. The ship was well-known for its deck, sail, and keel. It also had a compass that always pointed in the right direction."
The four things emphasized in the text- the deck, sail, keel, and compass- can all be symbolically brought together again when you collect the Puppis, Vela, Carina, and Pyxis coins (the deck, the sail, the keel, and the mariner's compass, respectively). All of these coins can be found scattered around the Twin Crevasses in the Zahhab Region, but none of them are in the Depths themselves.
The reward for completing this quest is an increase in company reputation and sixteen thousand pelagos.