The Tunnel (Spanish: El túnel) is a dark, psychological novel written by Argentine writer Ernesto Sabato about a deranged porteño painter, Juan Pablo Castel, and his obsession with a woman.

Missing out on an opportunity to approach her before she leaves the exhibition, he then spends the next few months obsessing over her, thinking of ways to find her in the immensity of Buenos Aires, and fantasizing about what to say to her.

This anxiety intensifies after he and Maria make a trip to an estancia, a country ranch in Mar del Plata owned by Allende's cousin Hunter.

The atmosphere, the presence and attitudes of the other visiting relatives, and realizing Hunter's jealousy all feed into Castel's paranoia, forcing him to flee the ranch with little more than a word to one of the service staff.

Upon returning home to Buenos Aires, Castel passionately composes a hurtful letter, accusing her of sleeping with Hunter, which he immediately regrets upon mailing to her.