The Old Fort or Purana Quila is one the oldest forts in Delhi, was built by Humayun and the foundation laid for the new capital, Dinpanah. Purana Qila and its environs flourished as the "sixth city of Delhi". The walls of the Fort rise to a height of 18 metres, traverse about 1.5 km, and have three arched gateways: the Bara Darwaza (Big Gate) facing west, which is still in use today; the south gate, also popularly known as the 'Humayun Gate' (probably so known because it was constructed by Humayun, or perhaps because Humayun's Tomb is visible from there); and lastly, the 'Talaqi Gate', often known as the "forbidden gate". All the gates are double-storeyed sandstone structures flanked by two huge semi-circular bastion towers, decorated with white and coloured-marble inlays and blue tiles.
The cache is hidden inside of the Fort, entrance fee is 10 Rupees for Indian geocachers and 100 Rupees for foreigners.. The site is open from sunrise to sunset.