Kan'eiji Temple (寛永寺), established in 1625, was one of the three Buddhist temples (Other two were Zojoji Temple in Tokyo and Rinnoji Temple in Nikko) where Tokugawa Shoguns' gorgeous tombs were erected.
The head monk of this temple was a post only a prince from the Imperial family could assume, and until the feudal times ended, this temple had been the very top temple of Tendai Buddhism.
The whole of present Ueno Park used be the grounds of Kan'eiji but after the temple was destroyed in the civil war of 1868, the precincts were converted into a public park and Kan'eiji itself was relocated to where it stands now.
The present main grounds of Kan'eiji are located to the northwest of the Tokyo National Museum and not so large. Around this area remain small gates of Gen'yuin Reibyo and Joken'in Reibyo, which are Tokugawa Shoguns' mausoleums (most of the components of these mausoleums were destroyed in WWII).
Konpon-chudo is the main hall of this temple. What's enshrined here is Yakushi Nyorai, a Buddhist god related to medicine. After the previous Konpon-chudo was destroyed in the civil war, this building, created in 1638, was relocated from Kitain Temple in present-day Kawagoe City, Saitama Prefecture.
This is one of the gates of Tokugawa shoguns' mausoleum created in 1709. Most parts of the mausoleum were lost during WWII.
This is another gate of Tokugawa shoguns' mausoleum created in 1679. Most part of this mausoleum were also burnt down during WWII.
Architecture in Ueno Park which belongs to Kan'eiji
Though most buildings of Kan'eiji were burned down in the civil war, some prepheral buildings still stand at its original location in Ueno Park.
What still remain as Kan'eiji's properties are Kiyomizu Kannondo, Shinobazu Bentendo, Ryo-daishi, and some more smaller buildings.
Shinto Shrines - Hanazono Inari Jinja and Ueno Toshogu - are now independent (See Ueno Toshogu.) A five-storied pagoda also remains in the Ueno Zoo (but is no longer in the possession of Kan'eiji.)
Kiyomizu Kannondo, a building dedicated to Senju Kannon Bosatsu, was constructed in 1631. Kannon Bosatsu is a Buddhist divinity of mercy, and Senju Kannon is a form of this divinity with a thousand hands. This construction is listed as an Important Cultural Property.
Shinobazu Bentendo, which enshrines goddess Benzaiten, was destroyed in WWII and reconstructed after the war. Benzaiten is a god of music, dance and fortune.
Ryo-daishi enshrines Tenkai, the founder of Kan'eiji, and Ryogen, a monk of the 10th century who rebuilt Tendai Buddhism. The main hall of this temple is new, but most of other buildings were built in the Edo period.
Five-story pagoda erected in 1639 remains in Ueno Zoo. It was donated to the Tokyo Metropolitan Government so it's no longer in the possesion of Kan'eiji.
There used to be many small temples affiliated to Kan'eiji in this area, and some still remain. Of these, Enshuin Temple has a not-so-large but a neat garden. It's situated near Kan'eiji so just take a look at it from the gate.