A fortress, whose crumbling ruins still exist today, dominated the center of the sixth city, Dinpanah. Purana Qila's main highlights are two buildings within its massive walls: Qila-I-Kuhna Masjid and the Sher Mandal. Sher Shah, who was in power briefly after displacing Humayun, built the former in 1541 in Afghan style.

It is an elegant construction in black and white marble, red sandstone and adorned with graceful arches. The Sher Mandal served as an observatory and library for Emperor Humayun, who later returned to power. This octagonal red sandstone building is where, in 1556, he plunged to his death down a steep flight of stairs, on his way to say his prayers. A climb to the top treats you to wonderful views of Delhi and the Yamuna River.