The Terrain Gallery, or the Terrain, is an art gallery and educational center at 141 Greene Street in SoHo, Manhattan, New York City. It was founded in 1955 with a philosophic basis: the ideas of Aesthetic Realism and the Siegel Theory of Opposites, developed by American poet and educator Eli Siegel. Its motto is a statement by Siegel: "In reality opposites are one; art shows this."