Seedbed.

“In this legendary sculpture/performance Acconci lay beneath a ramp built in the Sonnabend Gallery. Over the course of three weeks, he masturbated eight hours a day while murmuring things like, "You're pushing your cunt down on my mouth" or "You're ramming your cock down into my ass." Not only does the architectural intervention presage much of his subsequent work, but all of Acconci's fixations converge in this, the spiritual sphincter of his art. In Seedbed Acconci is the producer and the receiver of the work's pleasure. He is simultaneously public and private, making marks yet leaving little behind, and demonstrating ultra-awareness of his viewer while being in a semi-trance state.” – Jerry Saltz (via: http://www.ubu.com/film/acconci_seedbed.html)