Purana Qila, also known as the Old Fort, is a historic fort located in the heart of Delhi, India. The fort was built by the Afghan ruler Sher Shah Suri in the 16th century, on the site of the ancient city of Indraprastha, mentioned in the epic Mahabharata.

The fort has three main entrances, which are called the Humayun Darwaza, the Talaqi Darwaza, and the Bara Darwaza. It has walls that are 18 meters high and 1.5 kilometers in circumference. The fort is surrounded by a moat that used to be filled with water in the past.

Inside the fort, there are several notable structures, including the Qila-i-Kuhna Mosque, the Sher Mandal, and the Hammam. The Qila-i-Kuhna Mosque is a beautiful mosque built by Sher Shah Suri, which features intricate carvings and a large central dome. The Sher Mandal is a two-story octagonal tower that was built by the Mughal emperor Babur and later used as a library by Emperor Humayun. The Hammam is a bathhouse that was used by the Mughals for their ritualistic baths.

Purana Qila has been the site of several important historical events, including the battles fought between the Mughals and the British during the Indian Rebellion of 1857. Today, the fort is a popular tourist attraction and is maintained by the Archaeological Survey of India. Visitors can explore the various structures inside the fort and enjoy a beautiful view of the city from its walls.