Old Fort is Said to be built on the site of Indraprastha, mentioned in Mahabharata - the great Indian epic, Old Fort has been the seat for administration for many emperors. Now in ruins, this citadel had the glory of being the seat of the legendary ruler, Prithviraj Chauhan. Sher Shah Suri built it after he demolished the Humayun's city, Dinpanah. There are bastions on the corners of the western wall of the fort. The 2-km long ramparts of Purana Quila boast of three double-storied main gates sporting 'chhatris' on top. They can be found in north, south and west.

The northern one is called the 'Talaqi-Darwaza' (the Forbidden Gate) and has a carving of marble lions engaged in combat with a man in its front. One can still see the remnants of the colored tiles which used to ornament its exteriors. However, it is said that Sher Shah could not complete the construction of Old Fort and it was finished by Humayun. Thus, the southern gate of the fort is known as Humayun Darwaza. There is a wide moat on the northern and western sides of the fortress and a causeway connected the fortress with the main land.

Excavations in the Old Fort area have revealed pieces of painted greyware dated around 1000 BC, said to be related to Mahabharata. Relics and remains of later period found here confirm the belief that Purana Quila was built on the site of Indraprastha, the capital of Pandavas. These artifacts range from the Mauryan to early Mughal period, such as Northern Black polished ware, punch-marked coins, human and animal terracotta figurines and inscribed terracotta seals. Sher Shah built a mosque in 1541, with traits of Lodhi to Mughal architecture style.

Sher-Mandal, a double-storey octagonal tower of red sandstone and marble, surmounted by an octagonal chhatri and decorated with glazed tiles and painted plasterwork was also built by him. The latter was said to be used as a library by Humayun. It was from here that Humayun fell down and died. Besides these, there is a Sound and Light Show at Old Fort, presenting the 5000 years of history of Delhi. Other attractions near the Old Fort are a lake with paddle-boating facility and the Zoological Park situated just adjacent to it.