In the paper “Theatre Heterotopias: Sea on Stage”, the sea is discussed as a heterotopia per the term by M. Foucault, as a liminal ‘other place’ on stage, challenging the perception of theatre and reality. Sea redefines both the physical and the conceptual space, and as an element or an environment with transformative power that calls for a response installing, per Waldenfels, a presence of otherness. It evokes the question of (in)visibility, as examined by Merleau-Ponty, and of below-the-surface, neighbouring with Andrew Sofer’s Dark Matter. The possibilities of presenting sea as an ‘other’ space on stage are endless, from symbolic or abstract representation to the playful use of props, and from audiovisual projection to the literal use of water. Real water on stage challenges the boundaries between performance and reality; its special relationship with the body of the actor stimulates liveness in its double meaning (live material and event) triggering unusual audience response. In order to explore how the presence -or absence- of sea on stage affects both the concept and reception of the space and the bodies of the performers, examples from international productions such as Ariane Mnoushkine’s ‘Le dernier caravanserail’, Bob Wilson’s ‘Odyssey’, Eric Stube’s ‘Lady from the sea’, Simon McBurney’s ‘The Encounter’ and Ivo van Hove’s ‘Persona’ will be analysed, in relation to aesthetics and performance practice.