Torii gates are a distinctive feature of Japanese architecture, and in recent years some of them have been updated with elements of contemporary design; they’ve also become inspiration for other constructions.
Shinto is the indigenous religious system of the Japanese islands, which is broadly animist – in that everything has its own spirit or kami. Torii gates traditionally mark the entrances to Shinto temples and serve as a means of demarcating the sacred space. By passing through the gate the visitor is physically reminded that they are crossing some kind of boundary. The traditional form (see the final two pictures) is made of wood, painted vermilion and black. Stone gates are another traditional variant.
More recently, gates have been made of various metals, concrete, and other modern materials. The gates have also become inspiration for other pieces of public art and architecture, like the first few images above.
They’ve also become a pretty common symbol for Shinto (they are used on maps to mark Shinto temples) and Japanese culture more generally. They’ve been built in Second Life and used for inspiration for furniture.
I also included a picture of traditional torii gates at a shrine to Inari. Inari is the kami of fertility and industry, and it’s become customary for successful businesspeople to donate torii gates with their names on them to shrines to Inari. Thousands and thousands of them do this, producing these beautiful torii tunnels.