"Well...through the doors, Harry." -- Albus Dumbledore
There is a smaller antechamber connected to the Great Hall, door behind the teachers’ table, with a fireplace and many portraits (including that of the Fat Lady’s friend Violet) off the Great Hall (GF17)
"Harry went through the door out of the Great Hall, and found himself in a smaller room, lined with paintings of witches and wizards. A handsome fire was roaring in the fireplace opposite him" (GF17).