The sea, like an embryo or a foetus, seems to represent «a sort of first stage in the advancement of superior life forms». Its fluid character suggests an early age of our world's foundation, before fluid turns to stone. It appears as an archaic cosmos into which one descends in order to find hidden treasures in its depths. How did artisans work, shape, and integrate the varied materials of the sea into an artistic oeuvre? Which meanings were attached to these materials? When, how and why were the materials' fluid origin remembered?The sea can be considered the great global depot of the world, which includes objects of both great and ordinary character, illustrating ambitious and innocent aspirations to an equal extent. Moreover, the particular shininess of the oceanic materials, like pearls, shells or animals' skins, was usually associated with cosmic elements and thus emphasizes the pure and primal characters of these substances. The treasures of the sea were therefore beyond national. They were global. And their aquatic identity made them universal.Metaphorically speaking, the sea, as an object, has body, shape and even face, and is demarcated by earth and air. This amorphous entity has a solid bottom, its upper surface, namely face, touches the air, and its walls constantly struggle against solid substances such as rock and stone. In addition, its depths are unknown. There, in the heart of darkness, unconsciousness resides.This introductory essay aims at opening the so-called 'Pandora Box' of the fluid realm of the seas. It presents this space's great potential in providing us with vast amounts of historical information, usually 'lying concealed', as if under the water.