The Seireitei

Seireitei is a circular shiro with four main entrances, ten days walk apart, each guarded by one of the Gatekeepers. These gates are collectively called the Four Great Pure Soul Gates (Shidai Seireimon): these gates are made up of the Northern Black Ridge Gate (Kokuryōmon), the Eastern Blue Stream Gate (Shōryūmon), the Southern Red Hollow Gate (Shuwaimon), and the Western White Way Gate (Hakutōmon). The gates are so heavy that it takes the full might of Jidanbō Ikkanzaka to lift one, while during the Bount-led attack on Seireitei, siege machines were needed to open the gates. There are, however, doors within the gates, as seen when Momo Hinamori first entered the Shin'ō Academy.

The walls of Seireitei are made of Sekkiseki (Spirit Reducing Stone), a rare type of stone known to negate all Reiryoku, similar to magnetic lodestones. The stone also forms a spherical barrier around the city, extending above and below, stopping anything spiritual from breaching it from ground level, from the sky or from underground.

The wall that surrounds the Seireitei is commonly held up, only closing down when there is an emergency. When it is not down protecting the Seireitei, the wall protects the Soul King Palace, located in an inner dimension.

Information about the Seireitei is confidential. What is known is that in the center of the Seireitei is a white tower known as the Senzaikyū, where criminals are imprisoned; on the hill adjacent to it is the Sōkyoku, where prisoners are executed. Those permitted to live in the tranquility of the Seireitei are Shinigami and the Noble Houses. Shinigami live in the Division barracks, while high-ranking officers commute from their own homes.

The majority of the residents of Seireitei, nobility and Shinigami alike, do not interact with the citizens of Rukongai. However, residents of Rukongai, like Renji and Rukia, are allowed to apply for the Shin'ō Academy, which is often the only escape from the poorest conditions of Rukongai.

Following the Quincy War 1000 years ago, the Quincy who would later become the Wandenreich fled to the Seireitei and used Reishi to create space in the "shadows", effectively creating a world within the Seireitei, unseen to outsiders. These Quincy were able to move between their world and the Seireitei, as they were technically there to start with. The Wandenreich can absorb the Reishi particles of the Seireitei to reveal their hidden world.  The area is known as the Schatten Bereich, Shatten Beraihi; German and Japanese for "Shadow Realm"), which Yhwach cannot leave for more than a certain period of time before having to retreat.