Dominion Headquarters (also known as the Dominion Command Center) was a building on Cardassia Prime which housed the Dominion's high-ranking officials in the Alpha Quadrant and allowed them to plan the war after Terok Nor was retaken by the Federation. It was converted from a two-story building in Cardassia City.
Unlike the Cardassian War Room, Dominion Headquarters was more simplistic. The main room had a single monitor for displaying fleet movements and several consoles. At one end, the Female Changeling had a desk where she could sign documents. The ground level had a cargo bay. There were several living quarters for key personnel.
In 2375, Corat Damar led an attack on this facility, which was successful because the Female Changeling was forced to order Dominion forces to stand down and she was then taken into Federation custody. (DS9 short story: "Requital", DS9 episode: "What You Leave Behind")
Prior to Odo's transport down to Dominion Headquarters, he ordered Ensign Bremerton and five other Starfleet security officers from the USS Defiant to also transport to Dominion Headquarters and secure the facility. (DS9 novelization: What You Leave Behind)