Humayun's Tomb: A UNESCO World Heritage Site, Mughal Emperor Humayun is buried here. Surrounded by gardens, this tomb espouses the Islamic concept of 'Char Bagh'.
Chandni Chowk: Yes it's crowded, but it is an essential part of old Delhi. Shopping, eating, culture, Chandni Chowk offers everything. Do remember to check out the famous paranthe wali gali!
India Gate: A war memorial in central Delhi, it is surrounded by the seat of power in India. Just laze around in the gardens, eating ice cream, or walk to the Rashtrapati Bhavan, it makes for a good time. If you get bored, Connaught Place is nearby!
Lodhi Garden: Over 90 acres large, it contains many tombs, and is an architectural wonder. Of course, it is also a great place for picnics! Another alternative is Sundar Nursery.
DLF Promenade: A mall in Vasant Kunj, where you can find many luxury and mid-range brands, it is a great place to hangout and eat if you want to escape the Delhi heat.
So, how many places have you visited till now? Did we miss out something?