Torii is a gate, located at the entrance of the Shinto shrine. Torii is the boundary bewteen human and god's worlds.
Materials of the torii are usually wood, stone or copper but there are PVC, ceramic, stainless steel, concrete or iron made torii. Recently PVC made torii is increasing due to the cheap price and the endurance is much longer than other materials.
The torii of this picture is taken at Kamakura and it is located at the entrance of a street which connects Kamakura station and Tsurugaoka Hachimangu shrine. If the torii is not stone made, the color is usually red.