Nitenmon originally belonged to the Toshogu shrine in Ueno and was brought here after the rest of the shrine was destroyed, in 1642. By then, the gate was called Yadaijinmon.
Later two statues representing Buddhist guardians (called ten in Japanese) were brought here from the Tsurugaoka Hachiman-gu shrine of Kamakura, and thus the gate received its current name of Nitenmon, meaning "gate of two guardians". However, those statues were destroyed by fire at the end of WWII, and the guardians we see today were brought from another temple, the Kanei-ji of Ueno.
EXIF info:
Nikon D90
Lens: 8-16mm F/4.5-5.6G
Focal Length: 16mm
Aperture: F/6.3
Shutter Speed: 1/125s
ISO Sensitivity: ISO 200