Delhi's sights are spread across two very different cities. In Old Delhi, the essential stops are the Red Fort (Shah Jahan's 17th-century imperial palace), the Jama Masjid (India's largest mosque, from the same period), and the narrow lanes of Chandni Chowk between them. Plan a morning for each. Entrance is early; avoid midday heat.
The Mughal tomb belt running south across the city is the other great cluster: Humayun's Tomb (prototype for the Taj Mahal), the Qutub Minar complex (73-metre 12th-century sandstone tower surrounded by ruined mosques), Safdarjang's Tomb, and Lodhi Gardens where 15th-century tombs sit in one of the loveliest parks in India.
In New Delhi, the colonial-era India Gate and the Rajpath, the Jantar Mantar observatory, and the Bahá'í Lotus Temple are all worth visits. For museums, the National Museum holds the major collections of Indian antiquities, the Gandhi Smriti occupies the house where Gandhi was assassinated, and the Crafts Museum next to the Purana Qila is a wonderful survey of Indian village crafts.