Seireitei

The Seireitei is located in the center of the Soul Society. It is a circular shiro with four main entrances, ten days walk apart, each one guarded by a Gate Guardian. The walls of the Seireitei are made of Sekkiseki, a rare type of stone that is known to negate all reiatsu. 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.