Mar: Adentro

You use el because the word mar is the subject of the title.

A true story about Ramón Sampedro's 28-year campaign for the right to die with dignity. Mar adentro

While the film's title is often used without an article as a proper noun, if you are referring to it in a sentence (e.g., "The movie Mar Adentro "), the correct article to use is: Mar adentro Quick Grammar Facts Gender: Mar (sea) is generally masculine in Spanish. You use el because the word mar is the subject of the title