Short answers, pulled from the story.
Agra Fort was rebuilt by the Mughal emperor Akbar beginning in 1565, using red sandstone from the Barauli area of Rajasthan, and completed in 1573. Around 4,000 builders worked on it daily for eight years. An earlier fort on the same site was held by the Chauhan Rajputs and later by Sikandar Khan Lodi before the Mughals took it after the first Battle of Panipat in 1526.
Agra Fort was inscribed as a UNESCO World Heritage Site in 1983 because of its significance during Mughal rule. It served as the main residence of the Mughal dynasty's rulers until 1638 and contains palaces, gates, and structures spanning multiple emperors including Akbar, Jahangir, and Shah Jahan.
Shah Jahan was placed under house arrest in Agra Fort by his son Aurangzeb in 1658 after a war of succession. He spent eight years, from 1658 to 1666, imprisoned in the Muthamman Burj, an octagonal riverside tower with a direct view of the Taj Mahal. He died there in 1666 and his body was taken by boat to be buried at the Taj Mahal.
Jahangir's chain of justice, called Zanjir-i-Adl, was instituted around 1605 on the south side of the Muthamman Burj. It was a gold chain 80 feet long with 60 bells, weighing one quintal, stretched from the fort's Shah-Burj battlements to a stone post on the riverbank. Any aggrieved person could shake it to draw the emperor's attention directly, without fee or formality. The English traveller William Hawkins personally witnessed it.
The Ghaznin Gate is a wooden gate originally from the tomb of Mahmud Ghaznavi at Ghazni, brought to Agra Fort by the British in 1842. Lord Ellenborough falsely claimed it was the sandalwood gate of the Somnath temple taken by Mahmud in 1025. In fact, the gate is made of deodar wood from Ghazni. It stands 16.5 feet high and 13.5 feet broad, weighing about half a ton, and is stored in a room inside the fort.
Barely thirty Mughal buildings survive inside Agra Fort, all on the south-eastern riverside section. British troops of the East India Company demolished most of the original structures between 1803 and 1862 to build barracks, reducing what Abul Fazl had recorded as 500 buildings in the designs of Bengal and Gujarat.