An understanding of human mobility and cultural connectivity requires an accurate conception of that which facilitates maritime movement: the sea. The theory of “maritime cultural landscapes” has sought to address these questions from a landscape approach, and it is perhaps the most influential theory in maritime archaeology over the last thirty years. However, recent developments in philosophy challenge the cognitive-landscape theory underpinning the paradigm. This article examines these philosophies, the “flat ontologies” of Speculative Realism and Object-Oriented Ontology (OOO) and argues that they can be used to understand the sea as a new type of entity—a hyperobject. In this approach, the sea is not a landscape or facilitator of human activity but an entity of vast geographical and temporal scale that possesses agency. It argues for moving beyond idealist philosophies, such as cultural landscapes, toward the realist philosophy of OOO, including understanding the sea as a hyperobject.