Akasaka Hie Shrine
Akasaka Hie Jinja (日枝神社), a Shinto shrine located on the border of Nagatacho and Akasaka, had been worshiped as the spiritual guardian of Edo Castle ever since the castle was created in the 15th century.
For this reason, the Tokugawa shoguns of the 17th to 19th century, who placed their residence and government in the castle, considered it an important shrine and protected it. Even after the feudal times ended and Edo castle was turned into the Imperial Palace, it was regarded as the spiritual protector of the palace (at least before WWII). So it used to have a set of beautiful buildings, but almost all were lost in WWII and what stands now are post-war reconstructions made with concrete.
There are many Hie shrines in Japan, and along with Hiyoshi shrines, all can ulitimately be traced back to Hiyoshi Taisha Shrine in Shiga Prefecture.
Haiden is where you offer prayers.
Honden is where the divinities are enshrined.
Sanno Inari Jinja, constructed in 1659, is the only surviving building from the feudal times. It enshrines the landlord divinity of this precincts - this deity was situated here from before Hie Shrine was relocated here in 1659.
On Setsubun Day (Feb 3), many Shinto shrines and some large Buddhist temples hold bean-throwing events to drive away evil spirits.
Here at Akasaka Hie Shrine, a ritual is held from 11:30am and the bean-throwing takes place starts from around 0:00pm.
But the ritual from 11:30 is held inside the main building and you cannot see it at all from outside.
Sanno Matsuri (山王祭), held in mid-June, is the grand festival of this shrine. It's a renowned festival in Tokyo, but it's fully performed only in even-numbered years. For details about this event, see the article on the Sanno Matsuri at Akasaka Hie Shrine.