This roofed building contained 3 separate chambers:

(1) Lishkat Hagazit - Chamber of Hewed Stone

This chamber built with hewed stone served as the Supreme Court. Since it was forbidden to sit in the Azarah, the building was built half way in the Azarah and half way in the Cheil, and had entrances from both sides. Half of the building was built outside the Azarah where the judges would be allowed to sit.

(2) Lishkat Hagolah - The Chamber of the Well

A water wheel located in this chamber supplied a quick drink for the thirsty Kohanim. The Jews who came from the exile (Golah) dug this well.

(3) Lishkat Parhedrin - Chamber of the High Priest (Kohen Gadol)

Seven days before Yom Kippur, the High Priest would leave his mansion and family in the upper city and take up residence in this chamber. He would be instructed in the Yom Kippur service by the supreme court members and by the priestly scholars.
Parhedrin were government officials appointed for 1-year terms. This room was so named because during most of the 2nd Temple era, the High Priest who resided in this room was changed from year to year.