Short answers, pulled from the story.
Purana Qila originated as Dinpanah, a new city constructed by Mughal emperor Humayun near ancient Indraprastha ruins. The fort was later completed and strengthened by Sher Shah Suri after he defeated Humayun and seized the unfinished project.
Hem Chandra Vikramaditya was crowned in Purana Qila on the 7th of October 1556. This coronation marked a brief period of rule before the Mughals defeated him at the second battle of Panipat one month later.
By December 1942, there were 2,115 Japanese internees in the Purana Qila camp, the vast majority of whom came from Singapore. The camp housed over 2000 Japanese civilians including around 554 women and 224 children.
During the Partition of India in August 1947, Purana Qila became a refuge camp for over 150,000 to 200,000 Muslim refugees migrating to Pakistan. The camp remained functional until early 1948, serving as a temporary home for hundreds of thousands of displaced people.
Sher Shah Suri built the single-domed Qila-i-Kuhna Mosque in 1541 as a Jami Mosque for the Sultan and his courtiers. It is the best preserved building in Purana Qila and features early examples of the pointed arch in the region.
Humayun fell from the second floor of the Sher Mandal tower on the 24th of January 1556 and died of his injuries two days later. The tower served as a personal observatory and library for Humayun before his death.