After The Scattering, the Bene Gesserit's decided to continue to make Chapterhouse their permanent base of operations. The central located building on Chapterhouse housed the nerve center of the organization -- The Keep. A series of one to four story buildings, the sprawling complex blended in, and became one with the natural flora and fauna that surrounded it.
The Keep housed all of the barracks that the sisters and acolytes lived in, as well as the extensive library on human genetics and breeding patterns for the previous fifteen thousand years. Other parts of the Keep included the Sisterhood's school, weapons training facilities, and private quarters for the Gesserit's Reverend Mothers and other leaders.
The entire complex was built to be able to be packed and moved to another part of the world, or off-world, in a very short time, if needed.
After the merger of the Bene Gesserits with the Honored Matres, which produced the New Sisterhood, the Keep was kept as the organization's headquarters.