Jama Masjid is another marvelous treasure of the Old City, and is the largest mosque in India. Its courtyard can hold an incredible 25,000 devotees. The mosque took 13 years to build, and was completed in 1650. A strenuous climb to the top of its southern tower will reward you with a stunning view across the rooftops of Delhi. Be sure to dress appropriately when visiting the mosque or you won't be allowed in. This means covering your head, legs and shoulders. Attire is available there.