Japan, what is that row upon row of red doors called?

The door is called a torii. Torii are not necessarily red, although red is most common.?

Torii are pagoda-like Japanese shrine annexes that represent the entrance to a sacred realm and are used to distinguish between the sacred realm, where the gods reside, and the secular realm, where humans live. The presence of the torii reminds visitors that stepping into the torii means entering the divine realm, and that all subsequent behavior and actions should be taken with special care.

Senbon Torii is located in Fushimi Inari Taisha Shrine, a type of Japanese shrine building. The most impressive feature of Fushimi Inari Taisha Shrine is the Senbon Torii, which stretches for several kilometers up the mountain, an amazingly large group of more than 10,000 torii stretching all the way to the top of Mount Inari.

The Japanese believe that birds are the embodiment of the human soul, and that there are good souls as well as dirty souls among them, and that birds should not be allowed to approach shrines, so they build "kai" shaped pagodas called torii about 200 meters in front of the main gates of each shrine. When birds live here, they do not fly into the shrines.

It is said that "torii" is the distinction between the divine world and the earthly world, and when you step into the "torii", it means that you have entered the world of the gods, and you should pay special attention to all your behaviors.