Great Sept of Baelor
The Great Sept of Baelor, also called the Sept of Baelor, is the center of religious worship for the Faith of the Seven and the seat of the High Septon of the Faith. It is located in King's Landing, the capital of the Seven Kingdoms. It is named after the Septon King Baelor the Blessed.
The Great Sept of Baelor is named after the Septon King Baelor the Blessed. It is located at the top of Visenya's hill, surrounded by a white marble plaza. It features a statue of Baelor, which stands tall and serene upon his plinth; his face is a study of benevolence.  and large gardens, capable of holding hundreds surround the sept.
The sept itself is an impressive marble domed structure, It has 7 crystal towers, each of which has bells. Only on momentous occasions, such as the death of a king, are all of them rung. There are several sets of doors leading into the Sept, septons use the Father's Doors, septas the Mother's Doors and silent sisters the Stranger's Doors. Around the doors leading into the building is a raised marble pulpit from which a septon can address a gathering crowd.
Past the doors is the entrance hall of the sept, which is known as the Hall of Lamps. Those entering the hall walk beneath suspended globes of colored leaded glass. Through the double-doors is the sept-proper, with seven broad aisles which meet beneath the dome of glass, gold, and crystal. Its floors made out of marble and great windows of leaded, colored glass, and the seven altars are set about with candles. Different altars are used for different ceremonies, depending on their purpose. For example, marriages are always conducted at the altar between two towering gilded statues of the Father and the Mother.
A Game of Thrones
Eddard Stark is taken to the steps of the Great Sept of Baelor where, unbeknownst to him, Yoren, his daughter Arya Stark, and the disguised Ser Barristan Selmy were amongst the crowd. Eddard made a false public confession but the plan went awry when King Joffrey declared that Eddard must be executed, to the evident shock of Cersei, Varys, and the High Septon. Ilyn Payne beheaded Eddard Stark on the steps with his own greatsword, Ice.
A Clash of Kings
Thousands jam the Great Sept of Baelor prior to the Battle of the Blackwater. It is also mentioned several times that the Faith is outraged that Ned Stark's execution was performed there, as in their eyes, the sept was profaned with blood by this.
A Storm of Swords
A Feast for Crows
Lord Tywin Lannister's body rested under the Great Sept’s lofty dome of glass and gold and crystal, upon a stepped marble bier. At its head Jaime stood vigil. Lord Tywin Lannister's corpse stunk so badly no one had been able to enter the Great Sept of Baelor for days afterward.
A Dance with Dragons
Tyrion thinks that the red temple in Old Volantis has got to be 3 times the size of the Great Sept of Baelor. Cersei Lannister is imprisoned in a cell, high up in one of the 7 towers of the Great Sept of Baelor. During her walk of shame Cersei thinks to herself that to look at the statue of Baelor you’d never guess what a fool he’d been. She thinks it’s a wonder his statue does not crumble at the sight of her bare breasts. 
References and Notes
- A Dance with Dragons, Chapter 65, Cersei II.
- A Dance with Dragons, Chapter 32, Reek III.
- A Game of Thrones, Chapter 18, Catelyn IV.
- A Clash of Kings, Chapter 8, Tyrion II.
- A Dance with Dragons, Chapter 8, Tyrion III.
- A Storm of Swords, Chapter 59, Sansa IV.
- A Dance with Dragons, Chapter 67, The Kingbreaker.